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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16 of

the Securities Exchange Act of 1934

for the period ended 30 June 2016

Commission File Number 1-06262

BP p.l.c.

(Translation of registrant’s name into English)

1 ST JAMES’S SQUARE, LONDON, SW1Y 4PD, ENGLAND

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F  x            Form 40-F  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ¨

THIS REPORT ON FORM 6-K SHALL BE DEEMED TO BE INCORPORATED BY REFERENCE IN THE PROSPECTUS INCLUDED IN THE REGISTRATION STATEMENT ON FORM F-3 (FILE NOS. 333-208478 AND 333-208478-01) OF BP CAPITAL MARKETS p.l.c. AND BP p.l.c.; THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-67206) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-79399) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-103924) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-123482) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-123483) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-131583) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-131584) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-132619) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-146868) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-146870) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-146873) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-173136) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-177423) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-179406) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-186462) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-186463) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-199015) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-200794) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-200795) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-207188) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-207189) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-210316) OF BP p.l.c., THE REGISTRATION STATEMENT ON FORM S-8 (FILE NO. 333-210318) OF BP p.l.c., AND TO BE A PART THEREOF FROM THE DATE ON WHICH THIS REPORT IS FURNISHED, TO THE EXTENT NOT SUPERSEDED BY DOCUMENTS OR REPORTS SUBSEQUENTLY FILED OR FURNISHED.

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BP p.l.c. and subsidiaries

Form 6-K for the period ended 30 June 2016^(a)

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Group results second quarter and half year 2016

The commentaries above and following should be read in conjunction with the cautionary statement on page 40.

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Group headlines (continued)

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Analysis of RC profit (loss) before interest and tax

and reconciliation to profit (loss) for the period

Analysis of underlying RC profit before interest and tax

Reconciliations of underlying RC profit or loss to the nearest equivalent IFRS measure are provided on page 3 for the group and on pages 6-11 for the segments.

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Financial results

Sales and other operating revenues for the second quarter and half year were $8 billion and $16 billion respectively, compared with $11 billion and $23 billion for the corresponding periods in 2015. For the second quarter, revenues were lower mainly due to lower realizations and lower gas marketing and trading revenues. For the half year, the reduction was mainly due to lower realizations and lower gas marketing and trading revenues, partially offset by higher volumes.

The replacement cost loss before interest and tax for the second quarter and half year was $109 million and $1,314 million respectively, compared with a profit of $228 million and $600 million for the same periods in 2015. The second quarter and half year included a net non-operating gain of $7 million and a charge of $348 million respectively, compared with a net non-operating charge of $236 million and $478 million for the same periods a year ago. Fair value accounting effects in the second quarter and half year had an unfavourable impact of $145 million and $248 million respectively, compared with an unfavourable impact of $30 million and $20 million in the same periods of 2015.

After adjusting for non-operating items and fair value accounting effects, the underlying replacement cost result before interest and tax for the second quarter and half year was a profit of $29 million and a loss of $718 million respectively, compared with a profit of $494 million and $1,098 million for the same periods in 2015. The result for the second quarter and half year reflected lower liquids and gas realizations partly offset by lower costs reflecting the benefits of simplification and efficiency activities, lower rig cancellation costs, lower exploration write-offs, and lower depreciation, depletion and amortization expense.

Production

Production for the quarter was 2,090mboe/d, 1.0% lower than the second quarter of 2015. Underlying production* for the quarter increased by 1.5% mainly due to lower seasonal turnaround activity. For the first half, production was 2,259mboe/d, 2.3% higher than in the same period of 2015. First-half underlying production was broadly flat compared to first half 2015.

Key events

On 16 May BP announced it has doubled its interest in the Culzean development in the UK Central North Sea to 32%, following its acquisition of an additional interest from JX Nippon.

On 24 May BP and the State Oil Company of the Republic of Azerbaijan signed a memorandum of understanding to jointly explore potential prospects in Block D230 in the North Absheron basin in the Azerbaijan sector of the Caspian Sea.

On 25 May BP announced the start-up of a major water injection project at its Thunder Horse platform in the US Gulf of Mexico. The project will increase recovery of oil and natural gas from one of the field’s three main reservoirs.

On 9 June BP announced a gas discovery from the Baltim SW-1 exploration well in the Baltim South Development lease (BP 50% and Eni 50%, operator) in the East Nile Delta.

On 10 June BP and Det norske oljeselskap announced the creation of Aker BP ASA, an independent oil and gas company. Under the terms of the proposed transaction, the BP Norge and Det norske businesses will combine and be renamed Aker BP ASA which will be independently operated and listed on the Oslo Stock Exchange. Aker BP will be owned by current Det norske shareholder Aker (40%), other Det norske shareholders (30%) and BP (30%).

On 17 June BP and Rosneft signed final binding agreements, subject to regulatory approval, to create a new joint venture, Yermak Neftegaz LLC (Rosneft 51% and BP 49%). The joint venture will conduct onshore exploration within two Areas of Mutual Interest (AMIs) in the West Siberian and Yenisey-Khatanga basins in the Russian Federation, which cover a combined area of about 260,000 square kilometres.

On 20 June BP announced that together with the Egyptian Natural Gas Holding Company (EGAS), it has sanctioned development of the Atoll Phase One project, an early production scheme that will bring gas to the Egyptian domestic market, due to start in the first half of 2018. BP has a 100% interest in the concession.

In July BP, on behalf of Tangguh production-sharing agreement* (PSA) partners, announced the final investment decision has been approved for the development of the Tangguh expansion project in the Papua Barat province of Indonesia. The project will add a third LNG process train (Train 3), two offshore platforms, 13 new production wells, an expanded LNG loading facility, and supporting infrastructure.

This builds on the progress announced in our first-quarter results, which comprised the following: BP acquired interests in exploration licences in the Flemish Pass Basin offshore of Newfoundland, Canada; BP was awarded acreage in Norway at Skarv with partners Statoil, PGNiG and E.ON; BP and Oman Oil signed a heads of agreement with the government of the Sultanate of Oman, in relation to block 61; In Salah Gas, a Sonatrach, BP and Statoil joint venture, started up its Southern Fields project in Algeria; an exploration discovery was announced on the Nooros East prospect in Egypt, by the operator Eni who has tied it back for production; BP signed a framework agreement with Kuwait Petroleum Corporation to enhance

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recovery of existing oil and gas resources and explore possible other joint opportunities; BP and China National Petroleum Corporation signed a PSA for shale gas exploration, development and production in China; BP completed evaluation of the Kepler 3 discovery in the Gulf of Mexico with the aim to start production later this year; the Point Thomson project in Alaska, US, began production.

Outlook

Looking ahead, we expect third-quarter reported production to be lower than the second quarter due to seasonal turnaround and maintenance activities and the impact of the plant outage at the Enterprise Pascagoula gas processing plant in the Gulf of Mexico.

The commentary above contains forward-looking statements and should be read in conjunction with the cautionary statement on page 40.

Because of rounding, some totals may not agree exactly with the sum of their component parts.

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Financial results

Sales and other operating revenues for the second quarter and half year were $43 billion and $77 billion respectively, compared with $57 billion and $106 billion for the corresponding periods in 2015. The reduction in the second quarter and half year was mainly due to lower oil prices, partially offset by higher sales volumes.

The replacement cost profit before interest and tax for the second quarter and first half was $1,405 million and $3,285 million respectively, compared with $1,628 million and $3,711 million for the same periods in 2015.

The 2016 results include a net non-operating charge of $37 million for the second quarter and a net non-operating gain of $249 million for the half year, compared with a net non-operating charge of $122 million and $85 million for the same periods in 2015 (see pages 9 and 32 for further information on non-operating items). Fair value accounting effects had unfavourable impacts of $71 million for the second quarter and $290 million for the half year, compared with unfavourable impacts of $117 million and $229 million in the same periods of 2015.

After adjusting for non-operating items and fair value accounting effects, the underlying replacement cost profit before interest and tax for the second quarter and half year was $1,513 million and $3,326 million respectively, compared with $1,867 million and $4,025 million for the same periods in 2015.

Replacement cost profit before interest and tax for the fuels, lubricants and petrochemicals businesses is set out on page 9.

Fuels business

The fuels business reported an underlying replacement cost profit before interest and tax of $1,011 million for the second quarter and $2,327 million for the half year, compared with $1,394 million and $3,190 million for the same periods in 2015. The results for the quarter and half year reflect a significantly weaker refining environment, partially offset by lower costs from simplification and efficiency programmes, increased fuels marketing performance and strong refining operations. The half-year result was also impacted by a lower contribution from supply and trading, particularly in the first quarter.

During the first quarter of 2016 we completed the divestment of several non-strategic midstream assets in the US and Europe.

Lubricants business

The lubricants business reported an underlying replacement cost profit before interest and tax of $412 million for the quarter and $796 million for the half year, compared with $397 million and $742 million for the same periods in 2015. The quarter and half-year results reflect continued strong performance in growth markets and premium brands and lower costs from simplification and efficiency programmes. These factors contributed to a growth of more than 10% in the half-year underlying replacement cost profit before interest and tax, which was partially offset by adverse foreign exchange impacts.

During the second quarter of 2016 we sold approximately 11.5% from our 71% shareholding in Castrol India Limited.

Petrochemicals business

The petrochemicals business reported an underlying replacement cost profit before interest and tax of $90 million for the second quarter and $203 million for the half year, compared with $76 million and $93 million for the same periods in 2015. The result for the half year reflects stronger operations and margin optimization in a petrochemicals environment similar to the same period in 2015.

During the first quarter of 2016 we completed the sale of our Decatur petrochemicals complex in Alabama, US.

Outlook

In the third quarter we expect turnaround activity to remain high, at a similar level to the second quarter, and that industry refining margins will continue to be under significant pressure.

The commentary above contains forward-looking statements and should be read in conjunction with the cautionary statement on page 40.

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Rosneft

Replacement cost profit before interest and tax and underlying replacement cost profit before interest and tax for the second quarter and half year was $246 million and $312 million respectively, compared with $510 million and $693 million for the same periods in 2015. There were no non-operating items in the second quarter and half year of either year.

Compared with the same period last year, the result for the second quarter was primarily affected by lower oil prices. For the half year, the result was primarily affected by lower oil prices, partially offset by favourable foreign exchange effects.

BP’s two nominees, Bob Dudley and Guillermo Quintero, were re-elected to Rosneft’s board by the annual general meeting (AGM) on 15 June. The AGM also adopted a resolution to pay dividends of 11.75 roubles per ordinary share. BP expects to receive a dividend in relation to the 2015 annual results of approximately $335 million, after the deduction of withholding tax and subject to fluctuations in foreign exchange.

The commentary above contains forward-looking statements and should be read in conjunction with the cautionary statement on page 40.

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Other businesses and corporate

Other businesses and corporate comprises biofuels and wind businesses, shipping, treasury (which includes interest income on the group’s cash and cash equivalents), corporate activities including centralized functions, and the costs of the Gulf of Mexico oil spill.

Financial results

The replacement cost loss before interest and tax for the second quarter and half year was $5,525 million and $6,599 million respectively, compared with $11,202 million and $11,833 million for the same periods in 2015.

The second-quarter result included a net non-operating charge of $5,149 million, primarily relating to costs for the Gulf of Mexico oil spill, compared with a net charge of $10,801 million a year ago. Following significant progress in resolving outstanding claims, a reliable estimate has now been determined for all remaining material liabilities associated with the incident. The second-quarter charge reflects the recognition of additional provisions for these claims, including the cost of all remaining business economic loss claims under the 2012 Plaintiffs’ Steering Committee (PSC) settlement and the cost of resolving economic loss and property damage claims from individuals and businesses that either opted out of the PSC settlement and/or were excluded from that settlement. The second-quarter 2015 charge reflected a $9.8-billion charge associated with the settlement agreements signed in July 2015. For further information see Note 2 on page 17. For the half year, the net non-operating charge was $6,045 million, compared with a net non-operating charge of $11,142 million a year ago.

After adjusting for non-operating items, the underlying replacement cost loss before interest and tax for the second quarter and half year was $376 million and $554 million respectively, compared with $401 million and $691 million for the same periods in 2015. The half-year result reflects lower corporate costs and favourable foreign exchange impacts.

Gulf of Mexico oil spill

As previously disclosed, on 4 April 2016 the federal district court approved the Consent Decree between the United States, the Gulf states and BP which resolves all United States and Gulf states’ natural resource damages claims and Clean Water Act penalty claims, and certain other claims.

For further information see Note 2 on page 17 and Legal proceedings on page 38.

Biofuels

The net ethanol-equivalent production (which includes ethanol and sugar) for the second quarter was 283 million litres, compared with 247 million litres for the same period 2015.

Wind

Net wind generation capacity*(a) was 1,477MW at 30 June 2016 compared with 1,588MW at 30 June 2015. BP’s net share of wind generation for the second quarter and half year was 1,060GWh and 2,407GWh respectively, compared with 1,150GWh and 2,277GWh for the same periods in 2015.

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Financial statements

Group income statement