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Filed Pursuant to Rule 424(b)(5)
Registration No. 333-184882

The information in this prospectus supplement is not complete and may be changed. This prospectus supplement and the accompanying prospectus are part of an effective registration statement filed with the Securities and Exchange Commission. This prospectus supplement and the accompanying prospectus are not an offer to sell these securities and we are not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Subject to Completion

Preliminary Prospectus Supplement dated January 12, 2015

PROSPECTUS SUPPLEMENT

(To prospectus dated January 12, 2015)

20,260,000 Shares

Southwestern Energy Company

Common Stock

We are offering 20,260,000 shares of our common stock.

Our common stock is listed on the New York Stock Exchange under the symbol “SWN.” On January 9, 2015, the last reported sale price of our common stock was $24.68 per share.

Concurrently with this offering, we are making a public offering of 26,000,000 depositary shares, representing ownership interests in our         % Series B Mandatory Convertible Preferred Stock, par value $0.01, which we refer to as the “mandatory convertible preferred stock” (or up to 29,900,000 depositary shares if the underwriters in that offering exercise their over-allotment option in full), pursuant to a separate prospectus supplement and accompanying prospectus. We cannot assure you that the offering of depositary shares will be completed or, if completed, on what terms it will be completed. The offering of shares of our common stock pursuant to this prospectus supplement and the accompanying prospectus is not contingent upon the closing of our depositary shares offering, and the concurrent offering of our depositary shares is not contingent upon the closing of the offering of shares of our common stock hereunder.

Investing in our common stock involves risks. Please read “Risk Factors” beginning on page S-18 of this prospectus supplement and in the documents incorporated by reference in this prospectus supplement.

The underwriters may also exercise its option to purchase up to an additional 3,039,000 shares from us, at the price per share set forth above, for 30 days after the date of this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed on the adequacy or accuracy of this prospectus supplement or accompanying base prospectus. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the shares to the investors on or about January     , 2015.

Joint Book-Running Managers

The date of this prospectus supplement is January     , 2015.

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PROSPECTUS SUPPLEMENT

PROSPECTUS

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ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is the prospectus supplement, which describes the specific terms of this offering. The second part, the accompanying prospectus, including the documents incorporated by reference, provides more general information, some of which may not apply to this offering. The accompanying prospectus was filed as part of our registration statement on Form S-3 (Registration No. 333-184882) with the Securities and Exchange Commission (the “SEC”) on November 9, 2012 and a post-effective amendment dated January 12, 2015, as part of a “shelf” registration process. Under the shelf registration process, we may offer to sell debt securities, preferred or common stock and guarantees of debt securities, from time to time, in one or more offerings in an unlimited amount. Generally, when we refer to this prospectus supplement, we are referring to both parts of this document combined. We urge you to read carefully this prospectus supplement, the information incorporated by reference, the accompanying prospectus, and any free writing prospectus that we authorize to be distributed to you before buying any of the securities being offered under this prospectus supplement. This prospectus supplement may supplement, update or change information contained in the accompanying prospectus. To the extent that any statement that we make in this prospectus supplement is inconsistent with statements made in the accompanying prospectus or any documents incorporated by reference therein, the statements made in this prospectus supplement will be deemed to modify or supersede those made in the accompanying prospectus and such documents incorporated by reference therein.

Neither we nor the underwriters have authorized anyone to provide you with information that is different from that contained or incorporated by reference in this prospectus or in any free writing prospectus we may authorize to be delivered or made available to you. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. If information in this prospectus supplement is inconsistent with the accompanying prospectus, you should rely on this prospectus supplement. We are not, and the underwriters are not, making an offer of these securities in any state where the offer or sale is not permitted. You should not assume that the information provided by this prospectus supplement, the accompanying prospectus or the documents incorporated by reference in this prospectus supplement and in the accompanying prospectus is accurate as of any date other than their respective dates. Our business, financial condition, results of operations and prospects may have changed since those dates.

Before you invest in our common stock, you should carefully read the registration statement described in the accompanying prospectus (including the exhibits thereto) of which this prospectus supplement and the accompanying prospectus form a part, as well as this prospectus supplement, the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The incorporated documents are described in this prospectus supplement under “Incorporation by Reference.”

Unless otherwise indicated or the context otherwise requires, all references to “Southwestern,” “the Company,” “we,” “us” and “our” in this prospectus supplement refer to Southwestern Energy Corporation and its direct and indirect subsidiaries on a consolidated basis.

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INCORPORATION BY REFERENCE

The SEC allows us to “incorporate by reference” the information that we file with it, which means that we can disclose important information to you by referring you to other documents. The information incorporated by reference is an important part of this prospectus supplement, and information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference the following documents and all documents that we subsequently file with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) (other than the portions of those documents furnished under Item 2.02 or Item 7.01 and related exhibits thereto):

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FORWARD-LOOKING STATEMENTS

Certain statements and information in this prospectus supplement, the accompanying base prospectus and the documents incorporated by reference herein and therein may constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. The words “believe,” “expect,” “anticipate,” “plan,” “intend,” “foresee,” “should,” “would,” “could,” “attempt,” “appears,” “forecast,” “outlook,” “estimate,” “project,” “potential,” “may,” “will,” “are likely” and other similar expressions are intended to identify forward-looking statements, which are generally not historical in nature. These forward-looking statements are based on our current expectations and beliefs concerning future developments and their potential effect on us.

The forward-looking statements contained in this document are largely based on our expectations for the future, which reflect certain estimates and assumptions made by our management. These estimates and assumptions reflect our best judgment based on currently known market conditions, operating trends, and other factors. Although we believe such estimates and assumptions to be reasonable, they are inherently uncertain and involve a number of risks and uncertainties that are beyond our control. As such, management’s assumptions about future events may prove to be inaccurate. For a more detailed description of the risks and uncertainties involved, see “Risk Factors” beginning on page S-18 of this prospectus supplement and on page 2 of the accompanying prospectus, as well as “Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2013. We do not intend to publicly update or revise any forward-looking statements as a result of new information, future events, changes in circumstances, or otherwise. These cautionary statements qualify all forward-looking statements attributable to us, or persons acting on our behalf. Management cautions you that the forward-looking statements contained in this prospectus supplement, the accompanying prospectus or the documents incorporated by reference herein and therein are not guarantees of future performance, and we cannot assure you that such statements will be realized or that the events and circumstances they describe will occur. Factors that could cause actual results to differ materially from those anticipated or implied in the forward-looking statements herein include, but are not limited to:

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All written and oral forward-looking statements attributable to us are expressly qualified in their entirety by such factors. For additional information with respect to these factors, see “Incorporation by Reference.”

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MARKET AND INDUSTRY DATA

Market and industry data and forecasts included or incorporated by reference in this prospectus supplement have been obtained from independent industry sources as well as from research reports prepared for other purposes. Although we believe these third-party sources to be reliable, we have not independently verified the data obtained from these sources and we cannot assure you of the accuracy or completeness of the data. Forecasts and other forward-looking information obtained from these sources are subject to the same qualifications and uncertainties as the other forward-looking statements included or incorporated by reference in this prospectus supplement.

NON-GAAP FINANCIAL MEASURES

We refer to the term Adjusted EBITDA in this prospectus supplement. Adjusted EBITDA is defined as net income (loss) available to shareholders plus interest, income tax expense, non-cash impairment of natural gas and oil properties, (gain) loss on derivatives, net of settlements, and depreciation, depletion and amortization. This is a supplemental financial measure that is not prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). Any analysis of non-GAAP financial measures should be used only in conjunction with results presented in accordance with GAAP. We have included information concerning Adjusted EBITDA in this prospectus supplement because it is used by certain investors as a measure of the ability of a company to service or incur indebtedness and because it is a financial measure commonly used in our industry. Adjusted EBITDA should not be considered in isolation or as a substitute for net income (loss), net cash provided by operating activities or other income or cash flow data prepared in accordance with GAAP, or as a measure of our profitability or liquidity. Adjusted EBITDA as defined above may not be comparable to similarly titled measures of other companies. See “Summary—Summary Historical Consolidated Financial Data of the Company.” We also refer to pro forma Adjusted EBITDA in this prospectus supplement. Pro forma Adjusted EBITDA represents a further supplemental measure of our performance and ability to service debt. We prepare pro forma Adjusted EBITDA by further adjusting Adjusted EBITDA to give effect to recent acquisitions, as if those acquisitions had occurred on January 1, 2013. See “Summary—Summary Unaudited Pro Forma Condensed Combined Financial Data.”

We also refer to PV-10 and standardized measure in this prospectus supplement. PV-10 is a non-GAAP financial measure and means the estimated future gross revenue to be generated from the production of proved reserves, net of estimated production and future development costs, using prices and costs in effect as of the date of the report or estimate, without giving effect to non-property related expenses such as general and administrative expenses, debt service and future income tax expense or to depreciation, depletion and amortization, discounted using an annual discount rate of 10%. PV-10 is also referred to as “present value.” After-tax PV-10 is also referred to as “standardized measure” and is net of future income tax expense. Neither PV-10 nor standardized measure represents an estimate of fair market value of our oil and natural gas properties. PV-10 is used by the industry and our management as an arbitrary reserve asset value measure to compare against past reserve bases and the reserve bases of other business entities that are not dependent on the taxpaying status of the entity.

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RISK FACTORS

An investment in our common stock involves risks. You should consider carefully the following risks, as well as the risk factors discussed under the caption “Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2013, and our subsequent Quarterly Reports on Form 10-Q together with all of the other information included in, or incorporated by reference into, this prospectus supplement and the accompanying prospectus, when evaluating an investment in our common stock.

Risks Relating to our Common Stock

The market price of our common stock may be volatile or may decline and it may be difficult for you to resell shares of our common stock at prices you find attractive.

The market price of our common stock has historically experienced and may continue to experience volatility. For example, during the twelve months ended December 31, 2014, the high sales price per share of our common stock on the New York Stock Exchange was $49.16 and the low sales price per share was $26.75. The price of our common stock could be subject to wide fluctuations in the future in response to the following events or factors:

In particular, a significant or extended decline in natural gas and oil prices would have a material adverse effect on our financial position, our results of operations, our access to capital and the quantities of natural gas and oil that we can produce economically. For example, New York Mercantile Exchange, or NYMEX, natural gas prices traded at a high of $5.56 in February 2014 and a low of $3.73 in November 2014 based on last day of month settlements. Other risks described elsewhere under “Risk Factors” in this prospectus supplement and the accompanying prospectus and in the documents incorporated by reference in this prospectus supplement also could materially and adversely affect our share price.

The concurrent offering of our depositary shares, and the availability of our common stock for sale in the future, could reduce the market price of our common stock.

Concurrently with this offering, we are offering 26,000,000 depositary shares, plus up to 3,900,000 additional depositary shares if the underwriters in that offering exercise their over-allotment option to purchase

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additional depositary shares in full. This offering is not conditioned on the closing of the concurrent depositary shares offering, and the concurrent depositary shares offering is not conditioned on the closing of this offering.

Except as described herein under “Underwriting (Conflicts of Interest),” we are not restricted from issuing additional common stock, including securities that are convertible into or exchangeable for, or that represent the right to receive, common stock, including any common stock that may be issued upon the conversion of the mandatory convertible preferred stock (and, correspondingly, the depositary shares being offered concurrently with this offering). In the future, we may sell additional shares of our common stock to raise capital or acquire interests in other companies by using a combination of cash and our common stock or just our common stock. Any of these events may dilute your ownership interest in our company and have an adverse impact on the price of our common stock. In addition, a substantial number of shares of our common stock is reserved for issuance upon the exercise of stock options and upon conversion of the mandatory convertible preferred stock. Sales of a substantial number of shares of our common stock could depress the market price of our common stock and impair our ability to raise capital through the sale of additional equity securities. We cannot predict the effect that future sales of our common stock, or the perception that these sales may occur, or other equity-related securities would have on the market price of our common stock.

Purchasers in this offering will experience immediate dilution. If you purchase shares of common stock in this offering, you will pay more for your shares than the per share book value as of September 30, 2014.

The mandatory convertible preferred stock and the depositary shares may adversely affect the market price of our common stock.

The market price of our common stock is likely to be influenced by the mandatory convertible preferred stock and the depositary shares. For example, the market price of our common stock could become more volatile and could be depressed by:

Because we have no plans to pay dividends on our common stock, investors must look solely to stock appreciation for a return on their investment in us.

We do not currently pay cash dividends on our capital stock, and we do not anticipate paying cash dividends in the foreseeable future. We currently intend to retain all future earnings and other cash resources, if any, for the operation and development of our business and do not anticipate paying cash dividends in the foreseeable future. Payment of any future dividends will be at the discretion of our board of directors after taking into account many factors, including our financial condition, operating results, current and anticipated cash needs and plans for expansions. Any future dividends may also be restricted by any loan agreements which we may enter into from time to time and from the issuance of preferred stock should we decide to do so in the future.

Anti-takeover provisions in our organizational documents and under Delaware law may impede or discourage a takeover, which could cause the market price of our common stock to decline.

We are a Delaware corporation, and the anti-takeover provisions of Delaware law impose various impediments to the ability of a third party to acquire control of us, even if a change in control would be beneficial

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to our existing stockholders, which, under certain circumstances, could reduce the market price of our common stock. In addition, protective provisions in our Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws or the implementation by our board of directors of a stockholder rights plan could prevent a takeover, which could harm our stockholders.

Risks Relating to the Acquisitions

We may be subject to risks in connection with acquisitions, including the Acquisitions, and the integration of significant acquisitions may be difficult.

We have consummated the Chesapeake Acquisition and expect to consummate the other Acquisitions described above under the heading “Prospectus Supplement Summary— Recently Completed and Pending Acquisitions,” and we periodically evaluate other potential acquisitions of reserves, properties, prospects and leaseholds and other strategic transactions that appear to fit within our overall business strategy. The successful acquisition of producing properties, including the Acquisitions, requires an assessment of several factors, including:

The accuracy of these assessments is inherently uncertain. In connection with these assessments, we perform a review of the subject properties that we believe to be generally consistent with industry practices. Our review will not reveal all existing or potential problems nor will it permit us to become sufficiently familiar with the properties to fully assess their deficiencies and potential recoverable reserves. Inspections may not always be performed on every well, and environmental problems are not necessarily observable even when an inspection is undertaken. Even when problems are identified, the seller may be unwilling or unable to provide effective contractual protection against all or part of the problems. We often are not entitled to contractual indemnification for environmental liabilities and acquire properties on an “as is” basis, and, as is the case with certain liabilities associated with the assets to be acquired, we are entitled to indemnification for only certain environmental liabilities. In addition, we waived certain environmental and title indemnification in the Chesapeake Acquisition and did not include them in the Statoil Acquisition in exchange for downward adjustments to the purchase prices.

Significant acquisitions, including the Acquisitions, and other strategic transactions may involve other risks, including:

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The process of integrating operations could cause an interruption of, or loss of momentum in, the activities of our business. Members of our senior management may be required to devote considerable amounts of time to this integration process, which will decrease the time they will have to manage our business. If our senior management is not able to effectively manage the integration process, or if any significant business activities are interrupted as a result of the integration process, our business could suffer.

Financing the Acquisitions will substantially increase our leverage.

On December 22, 2014, we incurred aggregate borrowings of $5,000 million under the Bridge Facility and the Term Loan Facility to finance the Chesapeake Acquisition and to pay certain fees and expenses in connection with the Chesapeake Acquisition. We also intend to incur an aggregate of approximately $664 million under our revolving credit facility in order to consummate the WPX and the Statoil Acquisitions and an additional $200 million to fully pay the remaining borrowings under the Bridge Facility. We intend to partially repay amounts outstanding under the Bridge Facility, and if sufficient, the Term Loan Facility utilizing proceeds from the Securities Offerings and asset sales. Our total outstanding indebtedness as of September 30, 2014 was $1,807 million. As of January 9, 2015, after giving effect to the Chesapeake and the Statoil Acquisitions and the financing thereof, our total outstanding indebtedness increased by approximately $5,300 million. The increase in our indebtedness may reduce our flexibility to respond to changing business and economic conditions or to fund capital expenditures or working capital needs.

We may not be able to consummate the WPX and Statoil Acquisitions.

Although we entered into purchase and sale agreements for the WPX and the Statoil Acquisitions in December 2014, the consummation of each of them is subject to certain closing conditions, including conditions that must be met and are beyond our control. In addition, under certain circumstances we or the sellers may terminate the purchase agreements. There can be no assurances that either the WPX or the Statoil Acquisition will be consummated in the anticipated timeframe or at all.

If either the WPX or the Statoil Acquisition is not consummated under certain circumstances due to our default, we may forfeit the deposits under the respective purchase agreement. The aggregate deposit amount under the purchase agreements for the WPX and the Statoil Acquisitions is $65 million. Furthermore, our stock price could be negatively impacted if either the WPX or the Statoil Acquisitions are not consummated, regardless of the reason.

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USE OF PROCEEDS

We expect to receive gross proceeds from this offering of approximately $500 million, or $575 million if the underwriters exercise their option to purchase additional shares of common stock in full. After deducting the underwriting discounts and estimated offering expenses, net of reimbursement from the underwriters (based on an assumed price of $24.68 per share, which is the last reported sale price of our common stock on the New York Stock Exchange on January 9, 2014), we intend to use the net proceeds from this offering to partially repay amounts outstanding under our Bridge Facility entered into in connection with the Chesapeake Acquisition.

As of January 9, 2015, the outstanding balance under the Bridge Facility was $4,500 million, bearing an effective interest rate of approximately 1.55%, and the outstanding balance under the Term Loan Facility was $500 million, bearing an effective interest rate of approximately 1.52%. Amounts borrowed under the Bridge Facility and the Term Loan Facility were used to fund the Chesapeake Acquisition and costs and expenses related thereto. The Bridge Facility matures on December 18, 2015 and the Term Loan Facility matures on December 19, 2016.

The offering of shares of our common stock pursuant to this prospectus supplement and the accompanying prospectus is not contingent upon the closing of our depositary shares offering, and the concurrent offering of our depositary shares is not contingent upon the closing of the offering of shares of our common stock hereunder.

Affiliates of certain of the underwriters are lenders under the Bridge Facility and Term Loan Facility and revolving credit facility and as such will receive their pro rata share of the amounts used from the net proceeds of the Securities Offerings to repay indebtedness under such facilities. See “Underwriting (Conflicts of Interest).”

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CAPITALIZATION

The following table sets forth our cash and cash equivalents and capitalization as of September 30, 2014:

There can be no assurance that we complete the subsequent expected debt financing.

You should read our historical consolidated financial statements and notes, as well as our unaudited pro forma condensed combined financial statements related to the Chesapeake Acquisition and accompanying notes included in our Current Report on Form 8-K/A filed with the SEC on January 7, 2015, that are incorporated by reference into this prospectus supplement.

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DIVIDEND POLICY AND MARKET FOR COMMON STOCK

Dividend Policy

We do not currently pay cash dividends on our capital stock, and we do not anticipate paying cash dividends in the foreseeable future. Holders of our common stock may receive dividends when, as and if declared by our board of directors out of funds lawfully available for the payment of dividends. As a Delaware corporation, we may pay dividends out of surplus or, if there is no surplus, out of net profits for the fiscal year in which a dividend is declared and/or the preceding fiscal year. Section 170 of the Delaware General Corporation Law also provides that dividends may not be paid out of net profits if, after the payment of the dividend, capital is less than the capital represented by the outstanding stock of all classes having a preference upon the distribution of assets.

Price Range of Our Common Stock

The following table sets forth the high and low sales prices per share of our common stock as reported on the New York Stock Exchange since January 1, 2012.

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CONCURRENT OFFERING OF DEPOSITARY SHARES

Concurrently with this offering of shares of our common stock, we are offering, by means of a separate prospectus supplement and accompanying prospectus, 26,000,000 of our depositary shares (or 29,900,000 of our depositary shares, if the underwriters in that offering exercise their over-allotment option in full), each of which represents a 1/20th interest in a share of our     % Series B Mandatory Convertible Preferred Stock, par value $0.01, which we refer to in this prospectus supplement as our mandatory convertible preferred stock. We will deposit the shares of our mandatory convertible preferred stock represented by our depositary shares pursuant to a deposit agreement among us, Computershare Trust Company, N.A., acting as bank depositary, and the holders from time to time of the depositary shares. Each depositary share entitles the holder of such depositary share, through the bank depositary, to a proportional fractional interest in the rights and preferences of such share of mandatory convertible preferred stock, including conversion, dividend, liquidation and voting rights, subject to the terms of the deposit agreement.

The shares of mandatory convertible preferred stock will be convertible into an aggregate of up to              shares of our common stock (or up to              shares of our common stock, if the underwriters in that offering exercise their over-allotment option in full), in each case subject to anti-dilution, make-whole and other adjustments, as described in the prospectus supplement related to the offering of our depositary shares.

Affiliates of certain of the underwriters in the offering of our depositary shares are lenders under our Bridge and our Term Loan Facilities and will receive a portion of the net proceeds from that offering. Consequently, the offering of our depositary shares will be conducted in accordance with the requirements of FINRA Rule 5121.

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U.S. FEDERAL INCOME TAX CONSIDERATIONS TO NON-U.S. HOLDERS

The following discussion is a summary of the material U.S. federal income tax consequences to Non-U.S. Holders (as defined below) of the purchase, ownership and disposition of our common stock issued pursuant to this offering, but does not purport to be a complete analysis of all potential tax effects. The effects of other U.S. federal tax laws, such as estate and gift tax laws, and any applicable state, local or non-U.S. tax laws are not discussed. This discussion is based on the U.S. Internal Revenue Code of 1986, as amended (the “Code”), Treasury Regulations promulgated thereunder, judicial decisions, and published rulings and administrative pronouncements of the U.S. Internal Revenue Service (the “IRS”), in each case in effect as of the date hereof. These authorities may change or be subject to differing interpretations. Any such change or differing interpretation may be applied retroactively in a manner that could adversely affect a Non-U.S. Holder of our common stock. We have not sought and will not seek any rulings from the IRS regarding the matters discussed below. There can be no assurance the IRS or a court will not take a contrary position to those discussed below regarding the tax consequences of the purchase, ownership and disposition of our common stock.

This discussion is limited to Non-U.S. Holders that hold our common stock as a “capital asset” within the meaning of Section 1221 of the Code (generally, property held for investment). This discussion does not address all U.S. federal income tax consequences relevant to a Non-U.S. Holder’s particular circumstances, including the impact of the Medicare contribution tax on net investment income. In addition, it does not address consequences relevant to Non-U.S. Holders subject to special rules, including, without limitation:

If an entity treated as a partnership for U.S. federal income tax purposes holds our common stock, the tax treatment of a partner in the partnership will depend on the status of the partner, the activities of the partnership and certain determinations made at the partner level. Accordingly, partnerships holding our common stock and the partners in such partnerships should consult their tax advisors regarding the U.S. federal income tax consequences to them.

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THIS DISCUSSION IS FOR INFORMATIONAL PURPOSES ONLY AND IS NOT TAX ADVICE. INVESTORS SHOULD CONSULT THEIR TAX ADVISORS WITH RESPECT TO THE APPLICATION OF THE U.S. FEDERAL INCOME TAX LAWS TO THEIR PARTICULAR SITUATIONS AS WELL AS ANY TAX CONSEQUENCES OF THE PURCHASE, OWNERSHIP AND DISPOSITION OF OUR COMMON STOCK ARISING UNDER THE U.S. FEDERAL ESTATE OR GIFT TAX LAWS OR UNDER THE LAWS OF ANY STATE, LOCAL OR NON-U.S. TAXING JURISDICTION OR UNDER ANY APPLICABLE INCOME TAX TREATY.

Definition of a Non-U.S. Holder

For purposes of this discussion, a “Non-U.S. Holder” is any beneficial owner of our common stock that is neither a “U.S. person” nor an entity treated as a partnership for U.S. federal income tax purposes. A U.S. person is any person that, for U.S. federal income tax purposes, is or is treated as any of the following:

Distributions

As described in the section entitled “Dividend Policy and Market for Common Stock—Dividend Policy,” we do not anticipate declaring or paying dividends to holders of our common stock in the foreseeable future. However, if we do make distributions of cash or property on our common stock, such distributions will constitute dividends for U.S. federal income tax purposes to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. Amounts not treated as dividends for U.S. federal income tax purposes will constitute a return of capital and first be applied against and reduce a Non-U.S. Holder’s adjusted tax basis in its common stock, but not below zero. Any excess will be treated as capital gain and will be treated as described below under “—Sale or Other Taxable Disposition.”

Subject to the discussion below on effectively connected income, dividends paid to a Non-U.S. Holder of our common stock will be subject to U.S. federal withholding tax at a rate of 30% of the gross amount of the dividends (or such lower rate specified by an applicable income tax treaty, provided the Non-U.S. Holder furnishes a valid IRS Form W-8BEN or W-8BEN-E (or other applicable documentation) certifying qualification for the lower treaty rate). A Non-U.S. Holder that does not timely furnish the required documentation, but that qualifies for a reduced treaty rate, may obtain a refund of any excess amounts withheld by timely filing an appropriate claim for refund with the IRS. Non-U.S. Holders should consult their tax advisors regarding their entitlement to benefits under any applicable income tax treaty.

If dividends paid to a Non-U.S. Holder are effectively connected with the Non-U.S. Holder’s conduct of a trade or business within the United States (and, if required by an applicable income tax treaty, the Non-U.S. Holder maintains a permanent establishment in the United States to which such dividends are attributable), the Non-U.S. Holder will be exempt from the U.S. federal withholding tax described above. To claim the exemption, the Non-U.S. Holder must furnish to the applicable withholding agent a valid IRS Form W-8ECI, certifying that the dividends are effectively connected with the Non-U.S. Holder’s conduct of a trade or business within the United States.

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Any such effectively connected dividends will be subject to U.S. federal income tax on a net income basis at the regular graduated rates. A Non-U.S. Holder that is a corporation also may be subject to a branch profits tax at a rate of 30% (or such lower rate specified by an applicable income tax treaty) on such effectively connected dividends, as adjusted for certain items. Non-U.S. Holders should consult their tax advisors regarding any applicable tax treaties that may provide for different rules.

Sale or Other Taxable Disposition

A Non-U.S. Holder will not be subject to U.S. federal income tax on any gain realized upon the sale or other taxable disposition of our common stock unless:

Gain described in the first bullet point above generally will be subject to U.S. federal income tax on a net income basis at the regular graduated rates. A Non-U.S. Holder that is a corporation also may be subject to a branch profits tax at a rate of 30% (or such lower rate specified by an applicable income tax treaty) on such effectively connected gain, as adjusted for certain items.

A Non-U.S. Holder described in the second bullet point above will be subject to U.S. federal income tax at a rate of 30% (or such lower rate specified by an applicable income tax treaty) on any gain derived from the sale, which may be offset by U.S. source capital losses of the Non-U.S. Holder (even though the individual is not considered a resident of the United States), provided the Non-U.S. Holder has timely filed U.S. federal income tax returns with respect to such losses.

With respect to the third bullet point above, we believe that we currently are, and expect to remain for the foreseeable future, a USRPHC for U.S. federal income tax purposes. However, so long as our common stock is “regularly traded on an established securities market,” a Non-U.S. Holder will be subject to U.S. federal net income tax on a disposition of our common stock only if the Non-U.S. Holder actually or constructively holds or held (at any time during the shorter of the five-year period preceding the date of disposition or the Non-U.S. Holder’s holding period) more than 5% of our common stock. If our common stock is not considered to be so traded, a Non-U.S. Holder generally would be subject to U.S. federal income tax on the gain realized on a disposition of our common stock and generally would be required to file a U.S. federal income tax return, and a 10% withholding tax would apply to the gross proceeds from such sale.

Non-U.S. Holders should also consult their tax advisors regarding potentially applicable income tax treaties that may provide for different rules.

Information Reporting and Backup Withholding

Payments of dividends on our common stock will not be subject to backup withholding, provided the applicable withholding agent does not have actual knowledge or reason to know the Non-U.S. Holder is a United States person and the Non-U.S. Holder either certifies its non-U.S. status, such as by furnishing a valid IRS

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Form W-8BEN, W-8BEN-E or W-8ECI, or otherwise establishes an exemption. However, information returns are required to be filed with the IRS in connection with any dividends on our common stock paid to the Non-U.S. Holder, regardless of whether any tax was actually withheld. In addition, proceeds of the sale or other taxable disposition of our common stock within the United States or conducted through certain U.S.-related brokers generally will not be subject to backup withholding or information reporting, if the applicable withholding agent receives the certification described above and does not have actual knowledge or reason to know that such Non-U.S. Holder is a United States person, or the Non-U.S. Holder otherwise establishes an exemption. Proceeds of a disposition of our common stock conducted through a non-U.S. office of a non-U.S. broker generally will not be subject to backup withholding or information reporting.

Copies of information returns that are filed with the IRS may also be made available under the provisions of an applicable treaty or agreement to the tax authorities of the country in which the Non-U.S. Holder resides or is established.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules may be allowed as a refund or a credit against a Non-U.S. Holder’s U.S. federal income tax liability, provided the required information is timely furnished to the IRS.

Additional Withholding Tax on Payments Made to Foreign Accounts

Withholding taxes may be imposed under Sections 1471 to 1474 of the Code (such Sections commonly referred to as the Foreign Account Tax Compliance Act, or “FATCA”) on certain types of payments made to non-U.S. financial institutions and certain other non-U.S. entities. Specifically, a 30% withholding tax may be imposed on dividends on, or gross proceeds from the sale or other disposition of, our common stock paid to a “foreign financial institution” or a “non-financial foreign entity” (each as defined in the Code), unless (1) the foreign financial institution undertakes certain diligence and reporting obligations, (2) the non-financial foreign entity either certifies it does not have any “substantial United States owners” (as defined in the Code) or furnishes identifying information regarding each substantial United States owner, or (3) the foreign financial institution or non-financial foreign entity otherwise qualifies for an exemption from these rules. If the payee is a foreign financial institution and is subject to the diligence and reporting requirements in (1) above, it must enter into an agreement with the U.S. Department of the Treasury requiring, among other things, that it undertake to identify accounts held by certain “specified United States persons” or “United States-owned foreign entities” (each as defined in the Code), annually report certain information about such accounts, and withhold 30% on certain payments to non-compliant foreign financial institutions and certain other account holders. Foreign financial institutions located in jurisdictions that have an intergovernmental agreement with the United States governing FATCA may be subject to different rules.

Under the applicable Treasury Regulations, withholding under FATCA generally applies to payments of dividends, and will apply to payments of gross proceeds from the sale or other disposition of such stock on or after January 1, 2017.

Prospective investors should consult their tax advisors regarding the potential application of withholding under FATCA to their investment in our common stock.

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UNDERWRITING (CONFLICTS OF INTEREST)

Merrill Lynch, Pierce, Fenner & Smith Incorporated is acting as representative of each of the underwriters named below. Subject to the terms and conditions set forth in an underwriting agreement among us and the underwriters, we have agreed to sell to the underwriters, and each of the underwriters has agreed, severally and not jointly, to purchase from us, the number of shares of common stock set forth opposite its name below.

Subject to the terms and conditions set forth in the underwriting agreement, the underwriters have agreed, severally and not jointly, to purchase all of the shares sold under the underwriting agreement if any of these shares are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the nondefaulting underwriters may be increased or the underwriting agreement may be terminated.

We have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments the underwriters may be required to make in respect of those liabilities.

The underwriters are offering the shares, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel, including the validity of the shares, and other conditions contained in the underwriting agreement, such as the receipt by the underwriters of officer’s certificates and legal opinions. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Commissions and Discounts

The representative has advised us that the underwriters propose initially to offer the shares to the public at the public offering price set forth on the cover page of this prospectus and to dealers at that price less a concession not in excess of $     per share. After the initial offering, the public offering price, concession or any other term of the offering may be changed.

The following table shows the public offering price, underwriting discount and proceeds before expenses to us. The information assumes either no exercise or full exercise by the underwriters of their option to purchase additional shares.

The expenses of the offering, not including the underwriting discount, are estimated at $400,000 and are payable by us.

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Option to Purchase Additional Shares

We have granted an option to the underwriters, exercisable for 30 days after the date of this prospectus, to purchase up to 3,039,000 additional shares at the public offering price, less the underwriting discount. If the underwriters exercise this option, each will be obligated, subject to conditions contained in the underwriting agreement, to purchase a number of additional shares proportionate to that underwriter’s initial amount reflected in the above table.

No Sales of Similar Securities

We, our executive officers and directors have agreed not to sell or transfer any common stock or securities convertible into, exchangeable for, exercisable for, or repayable with common stock, for 90 days after the date of this prospectus without first obtaining the written consent of Merrill Lynch, Pierce, Fenner & Smith Incorporated. Specifically, we and these other persons have agreed, with certain limited exceptions, not to directly or indirectly

This lock-up provision applies to common stock and to securities convertible into or exchangeable or exercisable for or repayable with common stock. It also applies to common stock owned now or acquired later by the person executing the agreement or for which the person executing the agreement later acquires the power of disposition. Notwithstanding the above, this lock-up provision will not apply to us with respect to, among other things, (i) the common stock offered hereby, (ii) the depositary shares of our mandatory convertible preferred stock, our mandatory convertible preferred stock and any shares of our common stock into which the mandatory convertible preferred stock is convertible, issued in the concurrent offering of depositary shares of our mandatory convertible preferred stock, (iii) any shares of our common stock issued by us upon the exercise of an option or warrant or the conversion of a security outstanding on the date hereof and referred to in the accompanying prospectus or in this prospectus supplement, (iv) any shares of our common stock issued or options to purchase our common stock granted pursuant to existing employee benefit plans referred to in the accompanying prospectus or in this prospectus supplement, (v) any shares of our common stock issued upon conversion of the mandatory convertible preferred stock, (vi) any shares of our common stock issued and paid as a dividend on the mandatory convertible preferred stock and (vii) any shares of our common stock issued pursuant to any non-employee director stock plan or dividend reinvestment plan referred to in the accompanying prospectus or in this prospectus supplement. Notwithstanding the above, this lock-up provision will not apply to our directors and officers with respect to, among other things, and subject to certain additional limitations, (i) bona fide gifts, (ii) transfers to any trust for the direct or indirect benefit of our directors and officers or the immediate family of our directors and officers, (iii) distributions to limited partners or stockholders of such person or (iv) transfers to our directors’ and officers’ affiliates or to any investment fund or other entity controlled or managed by our directors and officers. In the event that either (x) during the last 17 days of the lock-up period referred to above, we issue an earnings release or material news or a material event relating to the Company occurs or (y) prior to the

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expiration of the lock-up period, we announce that we will release earnings results or become aware that material news or a material event will occur during the 16-day period beginning on the last day of the lock-up period, the restrictions described above shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event.

New York Stock Exchange Listing

The shares are listed on the New York Stock Exchange under the symbol “SWN.”

Price Stabilization, Short Positions

Until the distribution of the shares is completed, SEC rules may limit underwriters and selling group members from bidding for and purchasing our common stock. However, the representative may engage in transactions that stabilize the price of the common stock, such as bids or purchases to peg, fix or maintain that price.

In connection with the offering, the underwriters may purchase and sell our common stock in the open market. These transactions may include short sales, purchases on the open market to cover positions created by short sales and stabilizing transactions. Short sales involve the sale by the underwriters of a greater number of shares than they are required to purchase in the offering. “Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional shares described above. The underwriters may close out any covered short position by either exercising their option to purchase additional shares or purchasing shares in the open market. In determining the source of shares to close out the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase shares through the option granted to them. “Naked” short sales are sales in excess of such option. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of our common stock in the open market after pricing that could adversely affect investors who purchase in the offering. Stabilizing transactions consist of various bids for or purchases of shares of common stock made by the underwriters in the open market prior to the completion of the offering.

Similar to other purchase transactions, the underwriters’ purchases to cover the syndicate short sales may have the effect of raising or maintaining the market price of our common stock or preventing or retarding a decline in the market price of our common stock. As a result, the price of our common stock may be higher than the price that might otherwise exist in the open market. The underwriters may conduct these transactions on the New York Stock Exchange, in the over-the-counter market or otherwise.

Neither we nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our common stock. In addition, neither we nor any of the underwriters make any representation that the representatives will engage in these transactions or that these transactions, once commenced, will not be discontinued without notice.

Electronic Distribution

In connection with the offering, certain of the underwriters or securities dealers may distribute prospectuses by electronic means, such as e-mail.

Conflicts of Interest

As described in “Use of Proceeds,” we will use a portion of the net proceeds of this offering to repay outstanding borrowings under the Bridge Facility, Term Loan Facility and revolving credit facility. Because of the manner in which the proceeds will be used, the offering will be conducted in accordance with FINRA Rule 5121. In accordance with that rule, no “qualified independent underwriter” is required, because a bona fide public market exists in the shares, as that term is defined in the rule.

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Other Relationships

Some of the underwriters and their affiliates have engaged in, and may in the future engage in, investment banking and other commercial dealings in the ordinary course of business with us or our affiliates. They have received, or may in the future receive, customary fees and commissions for these transactions. In particular, an affiliate of Merrill Lynch, Pierce, Fenner & Smith Incorporated acts as the administrative agent and a lender, an affiliate of Citigroup Global Markets Inc., an affiliate of J.P. Morgan Securities LLC and an affiliate of Wells Fargo Securities, LLC act as co-syndication agents and lenders, an affiliate of BMO Capital Markets Corp. acts as a lender and Merrill Lynch, Pierce, Fenner & Smith Incorporated acted as sole lead arranger and sole bookrunner under the Bridge Facility. An affiliate of Merrill Lynch, Pierce, Fenner & Smith Incorporated acts as the administrative agent and the lender and Merrill Lynch, Pierce, Fenner & Smith Incorporated acted as sole lead arranger and sole bookrunner under the Term Loan Facility. An affiliate of J.P. Morgan Securities LLC acts as the administrative agent and a lender, an affiliate of Merrill Lynch, Pierce, Fenner & Smith Incorporated and an affiliate of Wells Fargo Securities, LLC act as co-syndication agents and lenders, an affiliate of Citigroup Global Markets Inc. acts as a co-documentation agent and a lender, an affiliate of BMO Capital Markets Corp. acts as a lender and J.P. Morgan Securities LLC, Merrill Lynch, Pierce, Fenner & Smith Incorporated, Wells Fargo Securities, LLC and Citigroup Global Markets Inc. acted as joint lead arrangers and joint lead bookrunners under our revolving credit facility. In addition, Merrill Lynch, Pierce, Fenner & Smith Incorporated, Citigroup Global Markets Inc., J.P. Morgan Securities LLC and Wells Fargo Securities, LLC are acting as underwriters of the concurrent offering of depositary shares of our mandatory convertible preferred stock and of the expected subsequent debt financing, for which they will receive customary fees and commissions. In addition, Merrill Lynch, Pierce, Fenner & Smith Incorporated acted as our financial advisor in connection with the Chesapeake Acquisition.

In addition, in the ordinary course of their business activities, the underwriters and their affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Reserved Share Program

At our request, the underwriters have reserved for sale, at the initial public offering price, up to 5% of the shares of common stock offered by this prospectus for sale to some of our directors and officers. If these persons purchase reserved shares it will reduce the number of shares of common stock available for sale to the general public. Any reserved shares that are not so purchased will be offered by the underwriters to the general public on the same terms as the other shares offered by this prospectus.

Selling Restrictions

Notice to Prospective Investors in the European Economic Area

In relation to each Member State of the European Economic Area (each, a “Relevant Member State”), no offer of shares may be made to the public in that Relevant Member State other than:

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Each person in a Relevant Member State who initially acquires any shares or to whom any offer is made will be deemed to have represented, acknowledged and agreed that it is a “qualified investor” within the meaning of the law in that Relevant Member State implementing Article 2(1)(e) of the Prospectus Directive. In the case of any shares being offered to a financial intermediary as that term is used in Article 3(2) of the Prospectus Directive, each such financial intermediary will be deemed to have represented, acknowledged and agreed that the shares acquired by it in the offer have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer of any shares to the public other than their offer or resale in a Relevant Member State to qualified investors as so defined or in circumstances in which the prior consent of the representative has been obtained to each such proposed offer or resale.

The Company, the representative and their affiliates will rely upon the truth and accuracy of the foregoing representations, acknowledgements and agreements.

This prospectus has been prepared on the basis that any offer of shares in any Relevant Member State will be made pursuant to an exemption under the Prospectus Directive from the requirement to publish a prospectus for offers of shares. Accordingly any person making or intending to make an offer in that Relevant Member State of shares which are the subject of the offering contemplated in this prospectus may only do so in circumstances in which no obligation arises for the Company or any of the underwriters to publish a prospectus pursuant to Article 3 of the Prospectus Directive in relation to such offer. Neither the Company nor the underwriters have authorized, nor do they authorize, the making of any offer of shares in circumstances in which an obligation arises for the Company or the underwriters to publish a prospectus for such offer.

For the purpose of the above provisions, the expression “an offer to the public” in relation to any shares in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the shares to be offered so as to enable an investor to decide to purchase or subscribe the shares, as the same may be varied in the Relevant Member State by any measure implementing the Prospectus Directive in the Relevant Member State and the expression “Prospectus Directive” means Directive 2003/71/EC (including the 2010 PD Amending Directive, to the extent implemented in the Relevant Member States) and includes any relevant implementing measure in the Relevant Member State and the expression “2010 PD Amending Directive” means Directive 2010/73/EU.

Notice to Prospective Investors in the United Kingdom

In addition, in the United Kingdom, this document is being distributed only to, and is directed only at, and any offer subsequently made may only be directed at persons who are “qualified investors” (as defined in the Prospectus Directive) (i) who have professional experience in matters relating to investments falling within Article 19 (5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended (the “Order”) and/or (ii) who are high net worth companies (or persons to whom it may otherwise be lawfully communicated) falling within Article 49(2)(a) to (d) of the Order (all such persons together being referred to as “relevant persons”). This document must not be acted on or relied on in the United Kingdom by persons who are not relevant persons. In the United Kingdom, any investment or investment activity to which this document relates is only available to, and will be engaged in with, relevant persons.

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Notice to Prospective Investors in Switzerland

The shares may not be publicly offered in Switzerland and will not be listed on the SIX Swiss Exchange (“SIX”) or on any other stock exchange or regulated trading facility in Switzerland. This document has been prepared without regard to the disclosure standards for issuance prospectuses under art. 652a or art. 1156 of the Swiss Code of Obligations or the disclosure standards for listing prospectuses under art. 27 ff. of the SIX Listing Rules or the listing rules of any other stock exchange or regulated trading facility in Switzerland. Neither this document nor any other offering or marketing material relating to the shares or the offering may be publicly distributed or otherwise made publicly available in Switzerland.

Neither this document nor any other offering or marketing material relating to the offering, the Company, the shares have been or will be filed with or approved by any Swiss regulatory authority. In particular, this document will not be filed with, and the offer of shares will not be supervised by, the Swiss Financial Market Supervisory Authority FINMA (FINMA), and the offer of shares has not been and will not be authorized under the Swiss Federal Act on Collective Investment Schemes (“CISA”). The investor protection afforded to acquirers of interests in collective investment schemes under the CISA does not extend to acquirers of shares.

Notice to Prospective Investors in the Dubai International Financial Centre

This prospectus supplement relates to an Exempt Offer in accordance with the Offered Securities Rules of the Dubai Financial Services Authority (“DFSA”). This prospectus supplement is intended for distribution only to persons of a type specified in the Offered Securities Rules of the DFSA. It must not be delivered to, or relied on by, any other person. The DFSA has no responsibility for reviewing or verifying any documents in connection with Exempt Offers. The DFSA has not approved this prospectus supplement nor taken steps to verify the information set forth herein and has no responsibility for the prospectus supplement. The shares to which this prospectus supplement relates may be illiquid and/or subject to restrictions on their resale. Prospective purchasers of the shares offered should conduct their own due diligence on the shares. If you do not understand the contents of this prospectus supplement you should consult an authorized financial advisor.

Notice to Prospective Investors in Australia

No placement document, prospectus, product disclosure statement or other disclosure document has been lodged with the Australian Securities and Investments Commission (“ASIC”), in relation to the offering. This prospectus does not constitute a prospectus, product disclosure statement or other disclosure document under the Corporations Act 2001 (the “Corporations Act”), and does not purport to include the information required for a prospectus, product disclosure statement or other disclosure document under the Corporations Act.

Any offer in Australia of the shares may only be made to persons (the “Exempt Investors”) who are “sophisticated investors” (within the meaning of section 708(8) of the Corporations Act), “professional investors” (within the meaning of section 708(11) of the Corporations Act) or otherwise pursuant to one or more exemptions contained in section 708 of the Corporations Act so that it is lawful to offer the shares without disclosure to investors under Chapter 6D of the Corporations Act.

The shares applied for by Exempt Investors in Australia must not be offered for sale in Australia in the period of 12 months after the date of allotment under the offering, except in circumstances where disclosure to investors under Chapter 6D of the Corporations Act would not be required pursuant to an exemption under section 708 of the Corporations Act or otherwise or where the offer is pursuant to a disclosure document which complies with Chapter 6D of the Corporations Act. Any person acquiring shares must observe such Australian on-sale restrictions.

This prospectus contains general information only and does not take account of the investment objectives, financial situation or particular needs of any particular person. It does not contain any securities

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recommendations or financial product advice. Before making an investment decision, investors need to consider whether the information in this prospectus is appropriate to their needs, objectives and circumstances, and, if necessary, seek expert advice on those matters.

Notice to Prospective Investors in Hong Kong

The securities have not been offered or sold and will not be offered or sold in Hong Kong, by means of any document, other than (a) to “professional investors” as defined in the Securities and Futures Ordinance (Cap. 571) of Hong Kong and any rules made under that Ordinance; or (b) in other circumstances which do not result in the document being a “prospectus” as defined in the Companies Ordinance (Cap. 32) of Hong Kong or which do not constitute an offer to the public within the meaning of that Ordinance. No advertisement, invitation or document relating to the securities has been or may be issued or has been or may be in the possession of any person for the purposes of issue, whether in Hong Kong or elsewhere, which is directed at, or the contents of which are likely to be accessed or read by, the public of Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to securities which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” as defined in the Securities and Futures Ordinance and any rules made under that Ordinance.

Notice to Prospective Investors in Japan

The securities have not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948, as amended) and, accordingly, will not be offered or sold, directly or indirectly, in Japan, or for the benefit of any Japanese Person or to others for re-offering or resale, directly or indirectly, in Japan or to any Japanese Person, except in compliance with all applicable laws, regulations and ministerial guidelines promulgated by relevant Japanese governmental or regulatory authorities in effect at the relevant time. For the purposes of this paragraph, “Japanese Person” shall mean any person resident in Japan, including any corporation or other entity organized under the laws of Japan.

Notice to Prospective Investors in Singapore

This prospectus has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of Non-CIS Securities may not be circulated or distributed, nor may the Non-CIS Securities be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275, of the SFA, or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the Non-CIS Securities are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

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securities (as defined in Section 239(1) of the SFA) of that corporation or the beneficiaries’ rights and interest (howsoever described) in that trust shall not be transferred within six months after that corporation or that trust has acquired the Non-CIS Securities pursuant to an offer made under Section 275 of the SFA except:

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LEGAL MATTERS

The validity of the issuance of the common stock covered by this prospectus supplement will be passed upon for Southwestern Energy Company by Latham & Watkins LLP, Houston, Texas. Certain legal matters in connection with this offering will be passed upon for the underwriters by Davis Polk & Wardwell LLP, New York, New York.

EXPERTS

The consolidated financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control Over Financial Reporting) incorporated in this prospectus supplement by reference to our Annual Report on Form 10-K for the year ended December 31, 2013 and the audited statements of revenues and direct operating expenses of the assets acquired in the Chesapeake Acquisition included as Exhibit 99.1 to our Current Report on Form 8-K/A dated January 7, 2015 have been so incorporated in reliance on the reports of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

Certain information with respect to the oil and gas reserves associated with our oil and gas prospects is derived from the reports of Netherland, Sewell & Associates, Inc., an independent petroleum consulting firm, and has been included in this prospectus supplement, and incorporated by reference herein, upon the authority of said firm as experts with respect to the matters covered by such reports and in giving such reports.

Certain information with respect to the oil and gas reserves associated with the assets acquired in the Chesapeake Acquisition is derived from the reports of that Netherland, Sewell & Associates, Inc., an independent petroleum consulting firm, and has been included in this prospectus supplement, and incorporated by reference herein, upon the authority of said firm as experts with respect to the matters covered by such reports and in giving such reports.

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GLOSSARY OF OIL AND GAS TERMS

We are in the business of exploring for and producing oil and natural gas. Oil and natural gas exploration is a specialized industry. Many of the terms used to describe our business are unique to the oil and natural gas industry. The following is a description of the meanings of some of the oil and natural gas industry terms used in this document.

Analogous reservoir. Analogous reservoirs, as used in resource assessments, have similar rock and fluid properties, reservoir conditions (depth, temperature, and pressure) and drive mechanisms, but are typically at a more advanced stage of development than the reservoir of interest and thus may provide concepts to assist in the interpretation of more limited data and estimation of recovery. When used to support proved reserves, analogous reservoir refers to a reservoir that shares all of the following characteristics with the reservoir of interest: (i) the same geological formation (but not necessarily in pressure communication with the reservoir of interest; (ii) the same environment of deposition; (iii) similar geologic structure; and (iv) the same drive mechanism.

Boe. One barrel of oil equivalent determined using the ratio of six Mcf of natural gas to one barrel of crude oil, condensate or natural gas liquids.

Bcf. One billion cubic feet of natural gas.

Bcfe. One billion cubic feet of natural gas equivalent, determined using the ratio of six Mcf of natural gas to one barrel of oil, condensate or NGLs.

Completion. The installation of permanent equipment for the production of oil, NGLs or natural gas.

Developed oil, NGL and natural gas reserves. Developed oil, NGL and natural gas reserves are reserves of any category that can be expected to be recovered: (i) through existing wells with existing equipment and operating methods or in which the cost of the related equipment is relatively minor compared to the cost of a new well; and (ii) through installed extraction equipment and infrastructure operational at the time of the reserves estimate if the extraction is by means not involving a well.

Development project. A development project is the means by which petroleum resources are brought to the status of economically producible. As examples, the development of a single reservoir or field, an incremental development in a producing field or the integrated development of a group of several fields and associated facilities with a common ownership may constitute a development project.

Economically producible. The term economically producible, as it relates to a resource, means a resource that generates revenue that exceeds, or is reasonably expected to exceed, the costs of the operation. The value of the products that generate revenue shall be determined at the terminal point of oil and natural gas producing activities.

Estimated ultimate recovery. Estimated ultimate recovery is the sum of reserves remaining as of a given date and cumulative production as of that date.

Exploitation. Optimizing oil, NGL and natural gas production from producing properties or establishing additional reserves in producing areas through additional drilling or the application of new technology.

Gas. Natural gas.

Gross acres or gross wells. The total acres or wells, as the case may be, in which a working interest is owned.

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Injection well or injection. A well which is used to place liquids or natural gases into the producing zone during secondary/tertiary recovery operations to assist in maintaining reservoir pressure and enhancing recoveries from the field.

Mcf. Thousand cubic feet of natural gas.

MBbls. One thousand barrels of crude oil.

MBoe. One thousand barrels of crude oil equivalent, determined using the ratio of six Mcf of natural gas to one barrel of oil, condensate or NGLs.

MMBoe. One million barrels of crude oil equivalent, determined using the ratio of six Mcf of natural gas to one barrel of oil, condensate or NGLs.

MMcf. One million cubic feet of natural gas.

MMcfe. One million cubic feet of natural gas equivalent, determined using the ratio of six Mcf of natural gas to one barrel of oil, condensate or NGLs.

Net acres or net wells. The sum of the fractional working interests owned in gross acres or wells, as the case may be.

Permeability. The ability, or measurement of a rock’s ability, to transmit fluids, typically measured in darcies or millidarcies. Formations that transmit fluids readily are described as permeable and tend to have many large, well-connected pores.

PV-10 or present value of estimated future net revenues. An estimate of the present value of the estimated future net revenues from proved oil, NGL and natural gas reserves at a date indicated after deducting estimated production and ad valorem taxes, future capital costs and operating expenses, but before deducting any estimates of federal income taxes. The estimated future net revenues are discounted at an annual rate of 10%, in accordance with the Securities and Exchange Commission’s practice, to determine their “present value.” The present value is shown to indicate the effect of time on the value of the revenue stream and should not be construed as being the fair market value of the properties. Estimates of future net revenues are made using oil and natural gas prices and operating costs at the date indicated and held constant for the life of the reserves.

Productive well. A well that is producing or is capable of production, including natural gas wells awaiting pipeline connections to commence deliveries and oil wells awaiting connection to production facilities.

Proved oil, NGL and natural gas reserves or Proved reserves. Proved oil, NGL and natural gas reserves are those quantities of oil, NGL and natural gas, which, by analysis of geoscience and engineering data, can be estimated with reasonable certainty to be economically producible from a given date forward, from known reservoirs, and under existing economic conditions, operating methods, and government regulation prior to the time at which contracts providing the right to operate expire, unless evidence indicates that renewal is reasonably certain, regardless of whether deterministic or probabilistic methods are used for estimation. The project to extract the hydrocarbons must have commenced, or the operator must be reasonably certain that it will commence the project, within a reasonable time.

The area of the reservoir considered as proved includes all of the following: (i) the area identified by drilling and limited by fluid contacts, if any; and (ii) adjacent undrilled portions of the reservoir that can, with reasonable certainty, be judged to be continuous with it and to contain economically producible oil, NGL and natural gas on the basis of available geoscience and engineering data.

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In the absence of data on fluid contacts, proved quantities in a reservoir are limited by the lowest known hydrocarbons as seen in a well penetration unless geoscience, engineering or performance data and reliable technology establish a lower contact with reasonable certainty. Where direct observation from well penetrations has defined a highest known oil elevation and the potential exists for an associated gas cap, proved oil reserves may be assigned in the structurally higher portions of the reservoir only if geoscience, engineering or performance data and reliable technology establish the higher contact with reasonable certainty.

Reserves which can be produced economically through application of improved recovery techniques (including, but not limited to, fluid injection) are included in the proved classification when: (i) successful testing by a pilot project in an area of the reservoir with properties no more favorable than in the reservoir as a whole, the operation of an installed program in the reservoir or an analogous reservoir or other evidence using reliable technology establishes the reasonable certainty of the engineering analysis on which the project or program was based; and (ii) the project has been approved for development by all necessary parties and entities, including governmental entities.

Existing economic conditions include prices and costs at which economic producibility from a reservoir is to be determined. The price shall be the twelve-month first day of the month historical average price during the twelve-month period prior to the ending date of the period covered by the report, determined as an unweighted arithmetic average of the first-day-of-the-month price for each month within such period, unless prices are defined by contractual arrangements, excluding escalations based upon future conditions.

Proved undeveloped reserves. Proved undeveloped oil, NGL and natural gas reserves are reserves that are expected to be recovered from new wells on undrilled acreage, or from existing wells where a relatively major expenditure is required for recompletion. Reserves on undrilled acreage are limited to those drilling units offsetting productive units that are reasonably certain of production when drilled. Proved reserves for other undrilled units are claimed only where it can be demonstrated with certainty that there is continuity of production from the existing productive formation. Estimates for proved undeveloped reserves will not be attributable to any acreage for which an application of fluid injection or other improved recovery technique is contemplated, unless such techniques have been proved effective by actual tests in the area and in the same reservoir.

Reasonable certainty. If deterministic methods are used, reasonable certainty means a high degree of confidence that the quantities will be recovered. If probabilistic methods are used, there should be at least a 90% probability that the quantities actually recovered will equal or exceed the estimate. A high degree of confidence exists if the quantity is much more likely to be achieved than not, and, as changes due to increased availability of geoscience (geological, geophysical and geochemical), engineering and economic data are made to estimated ultimate recovery with time, reasonably certain estimated ultimate recovery is much more likely to increase or remain constant than to decrease.

Reliable technology. Reliable technology is a grouping of one or more technologies (including computational methods) that have been field tested and have been demonstrated to provide reasonably certain results with consistency and repeatability in the formation being evaluated or in an analogous formation.

Reserves. Reserves are estimated remaining quantities of oil, NGLs and natural gas and related substances anticipated to be economically producible, as of a given date, by application of development projects to known accumulations. In addition, there must exist, or there must be a reasonable expectation that there will exist, the legal right to produce or a revenue interest in the production, installed means of delivering oil, NGLs and natural gas or related substances to market and all permits and financing required to implement the project.

Reservoir. A porous and permeable underground formation containing a natural accumulation of producible oil and/or natural gas that is confined by impermeable rock or water barriers and is individual and separate from other reservoirs.

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Resources. Resources are quantities of oil, NGLs and natural gas estimated to exist in naturally occurring accumulations. A portion of the resources may be estimated to be recoverable and another portion may be considered unrecoverable. Resources include both discovered and undiscovered accumulations.

Unconventional resource. A term used in the oil and natural gas industry to refer to a play in which the targeted reservoirs generally fall into one of four categories: (1) tight sands, (2) coal beds, (3) gas shales, or (4) oil shales. These reservoirs tend to cover large areas and lack the readily apparent traps, seals and discrete hydrocarbon-water boundaries that typically define conventional reservoirs. These reservoirs generally require fracture stimulation treatments or other special recovery processes in order to produce economic flow rates.

Undeveloped acreage. Lease acreage on which wells have not been drilled or completed to a point that would permit the production of commercial quantities of oil or natural gas regardless of whether or not such acreage contains proved reserves.

Undeveloped oil, NGL and natural gas reserves or Undeveloped reserves. Undeveloped oil, NGL and natural gas reserves are reserves of any category that are expected to be recovered from new wells on undrilled acreage, or from existing wells where a relatively major expenditure is required for recompletion. Reserves on undrilled acreage shall be limited to those directly offsetting development spacing areas that are reasonably certain of production when drilled, unless evidence using reliable technology exists that establishes reasonable certainty of economic producibility at greater distances. Undrilled locations can be classified as having undeveloped reserves only if a development plan has been adopted indicating that they are scheduled to be drilled within five years, unless the specific circumstances justify a longer time. Under no circumstances shall estimates for undeveloped reserves be attributable to any acreage for which an application of fluid injection or other improved recovery technique is contemplated, unless such techniques have been proved effective by actual projects in the same reservoir or an analogous reservoir, or by other evidence using reliable technology establishing reasonable certainty.

Working interest. The operating interest that gives the owner the right to drill, produce and conduct operating activities on the property and receive a share of production.

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PROSPECTUS

COMMON STOCK

PREFERRED STOCK

DEBT SECURITIES

DEPOSITARY SHARES

We may sell from time to time in one or more offerings:

Each time we offer and sell securities, we will provide a supplement to this prospectus that contains specific information about the offering and the amounts, prices and terms of the securities. The supplement may also add, update or change information contained in this prospectus with respect to that offering. You should carefully read this prospectus and the applicable prospectus supplement before you invest in any of our securities.

We may offer and sell the securities described in this prospectus and any prospectus supplement to or through one or more underwriters, dealers and agents, or directly to purchasers, or through a combination of these methods. If any underwriters, dealers or agents are involved in the sale of any of the securities, their names and any applicable purchase price, fee, commission or discount arrangement between or among them will be set forth, or will be calculable from the information set forth, in the applicable prospectus supplement. See the sections of this prospectus entitled “About this Prospectus” and “Plan of Distribution” for more information. No securities may be sold without delivery of this prospectus and the applicable prospectus supplement describing the method and terms of the offering of such securities.

INVESTING IN OUR SECURITIES INVOLVES RISKS. SEE THE “RISK FACTORS” ON PAGE 2 OF THIS PROSPECTUS AND ANY SIMILAR SECTION CONTAINED IN THE APPLICABLE PROSPECTUS SUPPLEMENT CONCERNING FACTORS YOU SHOULD CONSIDER BEFORE INVESTING IN OUR SECURITIES.

Our common stock is listed on the New York Stock Exchange under the symbol “SWN.” On January 9, 2015, the last reported sale price of our common stock on the New York Stock Exchange was $24.68 per share.

We will provide the specific terms of these securities in supplements to this prospectus. You should read this prospectus and the applicable supplement carefully before you invest.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is January 12, 2015

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Neither we nor the underwriters have authorized anyone to provide you with information that is different from that contained or incorporated by reference in this prospectus or in any free writing prospectus we may authorize to be delivered or made available to you. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. If information in this prospectus is inconsistent with the accompanying prospectus supplement, you should rely on the prospectus supplement. We are not, and the underwriters are not, making an offer of these securities in any state where the offer or sale is not permitted. You should not assume that the information provided by this prospectus or the documents incorporated by reference in this prospectus is accurate as of any date other than their respective dates. Our business, financial condition, results of operations and prospects may have changed since those dates.

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that Southwestern Energy Company filed with the Securities and Exchange Commission, or SEC, using a “shelf” registration process. Under this process, we may offer the securities described in this prospectus in one or more offerings. This prospectus provides you with a general description of the securities we may offer. Each time we offer securities, we will provide you with a prospectus supplement and any pricing supplement that will describe the specific amounts, prices and terms of the securities being offered. The prospectus supplement and pricing supplement may also add, update or change information contained in this prospectus. If there is any inconsistency between the information in this prospectus and the applicable prospectus supplement or pricing supplement, you should rely on the information in that prospectus supplement or pricing supplement. We may only use this prospectus to sell securities if it is accompanied by a prospectus supplement and any applicable pricing supplement.

To understand the terms of our securities, you should carefully read this document with the related prospectus supplement. Together they give the specific terms of the securities we are offering. You should also read the documents we have referred you to in “Where You Can Find More Information” and “Incorporation of Certain Information by Reference” below for information on our company and our financial statements before investing in our securities.

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In this prospectus, unless otherwise indicated or as the context otherwise requires, the terms “Southwestern Energy,” “SWN,” “we,” “us” and “our” refer to Southwestern Energy Company and its consolidated subsidiaries. Unless otherwise stated, currency amounts in this prospectus and any prospectus supplement are stated in United States dollars, or “$.”

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WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy any document we file at the SEC’s public reference room located at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the public reference room. Our SEC filings are also available to the public at the SEC’s website at http://www.sec.gov. You may also access the information we file electronically with the SEC through our website at http://www.swn.com. You may also inspect reports, proxy statements and other information about Southwestern Energy at the offices of the New York Stock Exchange, 20 Broad Street, New York, New York 10005.

This prospectus is part of a registration statement we have filed with the SEC relating to the securities. As permitted by SEC rules, this prospectus does not contain all of the information we have included in the registration statement and the accompanying exhibits we file with the SEC. You may refer to the registration statement and the exhibits for more information about the securities and us. The registration statement and the exhibits are available at the SEC’s public reference room or through the Internet.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” the information that we file with it, which means that we can disclose important information to you by referring you to other documents. The information incorporated by reference is an important part of this prospectus and information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference the following documents and all documents that we subsequently file with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) (other than the portions of those documents furnished under Item 2.02 or Item 7.01 and related exhibits thereto):

Any future filings that we make with the SEC, pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, for so long as the registration statement of which this prospectus is a part remains effective, shall be deemed to be incorporated by reference into this prospectus from the date such documents are filed (other than information in the documents or filings that is deemed not to be filed).

You may request a copy of these filings and any other documents incorporated by reference into this prospectus (excluding any exhibits to those filings unless the exhibit is specifically incorporated by reference into this filing) and a copy of the indenture and other agreements referred to in this prospectus, at no cost, by writing or telephoning us at the following address and telephone number:

Southwestern Energy Company

10000 Energy Drive,

Spring, Texas 77389

Attention: Investor Relations

Telephone: (832) 796-4700

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The above filings are also available to the public on our website at http://www.swn.com. (We have included our website address as an inactive textual reference and do not intend it to be an active link to our website. Information on our website is not part of this prospectus.)

ABOUT SOUTHWESTERN ENERGY COMPANY

Our Company

We are an independent energy company engaged in natural gas and oil exploration, development and production (E&P). We are also focused on creating and capturing additional value through our natural gas gathering and marketing businesses, which we refer to as Midstream Services. We conduct substantially all of our business through subsidiaries.

Corporate Information

Southwestern Energy is a Delaware corporation. Our principal executive offices are located at 10000 Energy Drive, Spring, Texas 77389, and our main telephone number at that location is (832) 796-4700. Our website is located at http://www.swn.com. We have not incorporated by reference into this prospectus the information included on, or linked from, our website (other than to the extent specified elsewhere herein), and you should not consider it to be a part of this prospectus.

RISK FACTORS

The securities to be offered by this prospectus may involve a high degree of risk. These risks will be set forth in the prospectus supplement relating to each such security. Certain risk factors relating to our business are set forth in the documents incorporated by reference into this prospectus. Those risk factors may be supplemented and amended by any risk factors set forth in a prospectus supplement. You should consider carefully those risk factors and the other information set forth elsewhere in this prospectus any applicable prospectus supplement or pricing supplement and the documents incorporated by reference herein when making any decision to invest in our securities. The occurrence of any of these risks might cause you to lose all or part of your investment in the offered securities.

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This prospectus contains or incorporates by reference statements that may be deemed to be forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). These statements appear in a number of places in the documents we incorporate by reference. All statements that address activities, outcomes and other matters that should or may occur in the future, including, without limitation, statements regarding the financial position, business strategy, production and reserve growth and other plans and objectives for our future operations, are forward-looking statements. Although we believe the expectations expressed in such forward-looking statements are based on reasonable assumptions, such statements are not guarantees of future performance. We have no obligation and make no undertaking to publicly update or revise any forward-looking statements, except as may be required by law.

Forward-looking statements include the items identified in the preceding paragraph, information concerning possible or assumed future results of operations and other statements contained or incorporated by reference in this prospectus identified by words such as “believe,” “expect,” “anticipate,” “plan,” “intend,” “foresee,” “should,” “would,” “could,” “attempt,” “appears,” “forecast,” “outlook,” “estimate,” “project,” “potential,” “may,” “will,” “are likely” and other similar expressions.

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You should not place undue reliance on forward-looking statements. They are subject to known and unknown risks, uncertainties and other factors that may affect our operations, markets, products, services and prices and cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. In addition to any assumptions and other factors referred to specifically in connection with forward-looking statements, risks, uncertainties and factors that could cause our actual results to differ materially from those indicated in any forward-looking statement include, but are not limited to: