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

UNDER THE SECURITIES EXCHANGE ACT OF 1934

July 20, 2016

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

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934:  ¨ Yes    x No

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): n/a

NEWS RELEASE

BHP BILLITON OPERATIONAL REVIEW

FOR THE YEAR ENDED 30 JUNE 2016

BHP Billiton Chief Executive Officer, Andrew Mackenzie, said: “Over the next 12 months, we expect volumes and costs across our minerals businesses to benefit from our continued drive to safely improve productivity. We can create significant value through further cost reductions, taking advantage of latent capacity in our assets and investing in low-capital projects. These initiatives are expected to grow production by five per cent in copper, up to four per cent in iron ore and three per cent in metallurgical coal in the next financial year.

“In Petroleum, we have delivered strong performance from our Conventional assets and responded to market conditions by reducing the number of rigs in our Onshore US assets as we focus on cash flow and value. We have taken advantage of the fall in deep water drilling costs and accelerated our conventional oil exploration program to simultaneously run campaigns in the Gulf of Mexico and the Caribbean. We are well positioned to bring on shale volumes as markets tighten and develop conventional resources over the medium to long term.”

Summary

Operational performance

Production for the 2016 financial year and guidance for the 2017 financial year are summarised in the table below.

Major development projects

At the end of the 2016 financial year, BHP Billiton had four major projects under development in Petroleum, Copper and Potash, with a combined budget of US$6.9 billion over the life of the projects.

During the year, first production was delivered by the North West Shelf Greater Western Flank-A petroleum project and the Greater Western Flank-B project was approved.

Corporate update

BHP Billiton expects Underlying attributable profit in the June 2016 half year to include additional items related to: (1) reversal of previously recorded inventory write-downs reflecting a slight recovery in commodity prices; (2) redundancies largely associated with the simplification of our business; and (3) impairments predominately in our Coal business.

In addition, the Group expects to record an exceptional item for global taxation matters between US$150 and US$200 million in the June 2016 half year. This includes potential litigation and tax-related amounts.

On 2 March 2016, Samarco Mineração S.A (Samarco), Vale S.A (Vale) and BHP Billiton Brasil LTDA (BHP Billiton Brasil) entered into an agreement with the Federal Government of Brazil, the States of Espirito Santo and Minas Gerais and certain other public authorities (Brazilian Authorities) (Framework Agreement). The Framework Agreement provides for settlement of claims brought by the Brazilian Authorities on 30 November 2015 seeking the establishment of a fund for clean-up costs and impacts relating to the Fundão tailings dam failure on 5 November 2015. The Framework Agreement provides for the restoration of the environment and communities affected by the Samarco dam failure. On 5 May 2016, the Framework Agreement was ratified by the Federal Court of Appeal in Brasilia.

On 3 May 2016, the Federal Prosecution Office commenced proceedings against Samarco, Vale and BHP Billiton Brasil for BRL155 billion for social, environmental and economic compensation relating to the Samarco dam failure. At the same time, the Federal Prosecution Office appealed the ratification of the Framework Agreement. On 30 June 2016, the Superior Court of Justice in Brazil, in the case initiated by Brazilian Authorities, issued an interim order suspending the decision of the Federal Court of Appeal to ratify the Framework Agreement. BHP Billiton Brasil intends to appeal the decision of the Superior Court of Justice.

Samarco and its shareholders continue to believe that the Framework Agreement provides the appropriate long-term remedial and compensation framework for responding to the impact of the Samarco tragedy and the platform for the parties to work together. As set out by the Framework Agreement, a private autonomous foundation (Foundation Renova) has been created to deliver the socioeconomic and environmental programs in the Agreement.

Samarco continues to deliver the programs covered by the Framework Agreement and 90 per cent of the 41 programs prescribed by the Framework Agreement have been initiated. Substantial progress has been made including: approximately two-thirds of the houses and buildings in the Mariana region have been completely rebuilt or restored; 800 hectares of emergency areas reforested along the rivers Doce, Carmo and Gualaxo; and 10 tributaries (46 hectares) of river margins have been cleaned and contoured between Bento Rodrigues and Barra Longa.

For the June 2016 half year, we are not yet in a position to provide an update to the potential financial impacts on BHP Billiton Brasil of the Samarco dam failure. We are continuing to work closely with Samarco and will provide an update as soon as we are in a position to do so. Any potential financial impacts related to the tragedy are expected to be classified as an exceptional item.

The guidance provided in this Operational Review will be updated should material information or events arise as the Group finalises its financial statements.

Marketing update

The average realised prices achieved for our major commodities are summarised in the table below. Iron ore shipments, on average, were linked to the index price for the month of shipment, with price differentials reflecting product quality. The majority of metallurgical coal and energy coal exports were linked to the index price for the month of shipment or sold on the spot market, with price differentials reflecting product quality.

At 30 June 2016, the Group had 316 kt of outstanding copper sales that were revalued at a weighted average price of US$2.20 per pound. The final price of these sales will be determined in the 2017 financial year. In addition, 363 kt of copper sales from the 2015 financial year were subject to a finalisation adjustment in the current period. The provisional pricing and finalisation adjustments will decrease earnings before interest and tax by US$260 million in the 2016 financial year.

Petroleum

Production

Total petroleum production – Total petroleum production for the 2016 financial year decreased by six per cent to 240 MMboe. Petroleum production is forecast to decrease to between 200 and 210 MMboe in the 2017 financial year.

In Onshore US, we continue to focus on near-term cash flow performance. A reduction in capital expenditure and development activity is expected to lead to a decline in volumes to between 77 and 83 MMboe in the 2017 financial year. In our Conventional business, volumes are expected to decrease to between 123 and 127 MMboe as a result of the divestment of our gas business in Pakistan and natural field decline.

Crude oil, condensate and natural gas liquids – Crude oil, condensate and natural gas liquids production for the 2016 financial year decreased by seven per cent to 116 MMboe.

Onshore US liquids volumes declined by 13 per cent to 48 MMboe as increased liquids production from the Permian partially offset the temporary deferral of completions activity in the Black Hawk and drilling activity in the Hawkville. Completions activity in the Black Hawk resumed late in the June 2016 quarter.

Conventional liquids volumes were broadly unchanged as new production wells at Atlantis, Mad Dog and Pyrenees offset natural field decline across the portfolio, cessation of production at Stybarrow, maintenance at North West Shelf and industrial action at Bass Strait.

Natural gas – Natural gas production for the 2016 financial year declined by five per cent to 745 bcf.

The decline primarily reflects lower Onshore US gas volumes as a result of the decision to defer development activity for longer-term value and the successful divestment of our gas business in Pakistan as we continue to create a more focused portfolio. This was partially offset by higher demand at Bass Strait and Macedon.

Projects

Petroleum capital expenditure for the 2016 financial year declined by approximately 50 per cent to US$2.5 billion. A further 44 per cent reduction to approximately US$1.4 billion is planned for the 2017 financial year. This includes Conventional capital expenditure of US$0.8 billion, which remains focused on high-return infill drilling opportunities in the Gulf of Mexico and life extension projects at Bass Strait and North West Shelf.

Onshore US development activity

Onshore US drilling and development expenditure for the 2016 financial year was approximately US$1.2 billion, of which approximately US$400 million related to a reduction in capital creditors. Our operated rig count declined from five to four in the June 2016 quarter as we continue to focus on value maximisation and cash flow performance. Onshore US capital expenditure is expected to be approximately US$600 million in the 2017 financial year with development activity tailored to market conditions.

Petroleum exploration

Exploration and appraisal wells drilled during the June 2016 quarter are summarised below.

During the June 2016 quarter, BHP Billiton acquired 91 blocks with no well obligations in the Gulf of Mexico: a Lease Exchange Agreement was executed with Chevron for 61 blocks; a Sale and Purchase Agreement was executed with ConocoPhillips for 26 blocks; and regulatory approval was received for four blocks awarded in Lease Sale 241 in March 2016. In Australia, the Bunyip and Tallaganda Retention Leases WA-71-R and WA-72-R were awarded and the Tallaganda Exploration Lease WA-351-P expired.

Petroleum exploration expenditure for the 2016 financial year was US$590 million, of which US$273 million was expensed. Activity for the period was largely focused on our core areas in the deepwater Gulf of Mexico, the Caribbean and the Northern Beagle sub-basin off the coast of Western Australia, where we acquired additional acreage, seismic data and increased drilling activity. Our exploration activity has increased in the Gulf of Mexico following the positive exploration well results at Shenzi North and drilling has commenced in Trinidad and Tobago. We are pursuing high-quality oil plays in our three priority basins and a US$700 million exploration program is planned for the 2017 financial year as we accelerate testing of our future growth opportunities.

Copper

Production

Copper – Total copper production for the 2016 financial year decreased by eight per cent to 1.6 Mt as improved operating performance across the copper operations was offset by the grade-related volume decline at Escondida. Total copper production is forecast to increase to 1.7 Mt in the 2017 financial year.

Escondida copper production for the 2016 financial year decreased by 20 per cent to 979 kt. Record cathode production and record material mined, together with Organic Growth Project 1 reaching full capacity in the June 2016 quarter, was more than offset by a 28 per cent decline in grade, as expected. Following this strong operating performance, we expect unit costs at Escondida to be slightly below guidance of US$1.21 per pound for the 2016 financial year(2). The Escondida Bioleach Pad Extension project, which includes the expansion of the leach pad to four layers, was completed during the March 2016 quarter and has also contributed to the operating cost improvement.

The Escondida Owners Council approved an investment of US$180 million (100 per cent basis) for the Los Colorados Extension project in June 2016. First production is expected in the second half of the 2017 financial year, adding incremental capacity of approximately 200 ktpa in the near term. Copper production of 1,070 kt is expected in the 2017 financial year as the Escondida Water Supply project is commissioned in the second half of the year and enables the utilisation of three concentrators.

Pampa Norte copper production for the 2016 financial year increased by one per cent to 251 kt, supported by record ore milled and higher grades at Spence. Copper production is expected to increase in the 2017 financial year with the completion of the Spence Recovery Optimisation (SRO) project which will enable the full utilisation of the 200 ktpa tankhouse. SRO is expected to ramp up during the September 2016 quarter and achieve an annualised production rate of 200 kt from the December 2016 quarter. The Spence Growth Option remains in feasibility with the potential to extend mining operations by more than 50 years and increase copper capacity by approximately 200 ktpa. Final Board review is expected in the second half of the 2017 calendar year.

Olympic Dam copper production for the 2016 financial year increased by 63 per cent to 203 kt. This strong performance reflected higher grades and improved smelter and mill utilisation after the Svedala mill outage in the prior year and came despite planned smelter maintenance during the June 2016 quarter. Copper production in the 2017 financial year is expected to remain broadly unchanged from the 2016 financial year.

Antamina copper production for the 2016 financial year increased by 36 per cent to a record 146 kt as it benefitted from higher grades and higher mill throughput. Copper production is expected to decrease in the 2017 financial year to approximately 130 kt, as mining progresses through a zinc rich ore zone consistent with the mine plan. Zinc production is expected to increase from 55 kt to approximately 90 kt in the 2017 financial year.

Projects

Iron Ore

Production

Iron ore – Total iron ore production for the 2016 financial year was broadly unchanged at 227 Mt as record production at WAIO offset the suspension of operations at Samarco. Total iron ore production is expected to increase to between 228 and 237 Mt in the 2017 financial year, excluding production from Samarco.

WAIO production for the 2016 financial year increased by two per cent to a record 257 Mt (100 per cent basis) as the Jimblebar mining hub operated at full capacity and utilisation at the Newman ore handling plant improved. This more than offset one-off operational issues in the December 2015 quarter, the impact of adverse weather conditions and the initiation of a rail renewal and maintenance program in the June 2016 half year. Following a strong recovery from the wet season, WAIO produced at an annualised rate of 275 Mt in June 2016.

WAIO production for the 2017 financial year is forecast to increase to between 265 and 275 Mt (100 per cent basis). The 24 month rail program, which will support the integrated supply chain’s long-term reliability, is progressing on schedule. Along with our focus on productivity and the ramp-up of additional capacity at the Jimblebar mining hub, this will deliver an increase in system capacity to 290 Mtpa in the 2019 financial year. The installation of the new primary crusher and additional conveying capacity at Jimblebar is expected to be completed in the December 2016 quarter.

Samarco production for the 2016 financial year was 11 Mt (100 per cent basis). Mining and processing operations at Samarco remain suspended following the failure of the Fundão tailings dam and Santarém water dam on 5 November 2015. Sales from the final shipment of pellets from stockpiles were settled in the June 2016 quarter.

Coal

Production

Metallurgical coal – Metallurgical coal production for the 2016 financial year increased by one per cent to a record 43 Mt. Metallurgical coal production is expected to increase to 44 Mt in the 2017 financial year despite the planned divestment of IndoMet Coal.

Queensland Coal production was flat as record production at five mines, underpinned by increased plant and equipment availability and utilisation, offset the completion of longwall mining at Crinum, a convergence event at the Broadmeadow mine and unfavourable weather conditions. Record quarterly production resulted in a 17 per cent increase in volumes from the March 2016 quarter.

Queensland Coal production is forecast to increase to 44 Mt in the 2017 financial year. This improvement will be supported by delivering higher wash-plant and truck hours which will more than offset the closure of Crinum. A longwall move at Broadmeadow and wash-plant shutdown at Saraji are scheduled for the September 2016 quarter.

First production from the Haju mine in Indonesia was achieved during the 2016 financial year. On 7 June 2016, BHP Billiton entered into an agreement to sell its 75 per cent interest in IndoMet Coal to its equity partner PT Alam Tri Abadi (Adaro). Completion of the sale is conditional upon the fulfilment of customary regulatory approvals.

Energy coal – Energy coal production for the 2016 financial year decreased by 16 per cent to 34 Mt. Energy coal production is forecast to decrease to 32 Mt in the 2017 financial year as productivity improvements at New South Wales Energy Coal partially offset the divestment of our New Mexico Coal assets.

New South Wales Energy Coal production for the 2016 financial year declined by 13 per cent due to the impact of heavy rainfall, the progression through a higher strip ratio zone and rescheduling of the mine plan based on individual pit economics. Cerrejón volumes declined by 11 per cent as drought conditions in the first nine months of the year followed by heavy rainfall in the June 2016 quarter constrained production.

Navajo Coal production for the 2016 financial year decreased by 18 per cent as a result of lower customer demand. The transfer of management and operatorship for Navajo Coal to Navajo Transitional Energy Company remains on track for 31 December 2016. The sale of the San Juan Mine to Westmoreland Coal Company was completed on 31 January 2016.

Other

Nickel production

Nickel – Nickel West production for the 2016 financial year decreased by 10 per cent to 81 kt and reflected planned major maintenance outages at the Kalgoorlie smelter and Kwinana refinery during the December 2015 quarter, and a reduction in third party ore delivered to the Kambalda concentrator. Higher nickel matte production during the June 2016 quarter was supported by additional third party concentrate purchases.

Nickel production is expected to increase by approximately 10 per cent in the 2017 financial year, with higher grade ore at Mt Keith and a ramp up in mining at Leinster since February 2016 supporting higher utilisation rates at the Kalgoorlie smelter and Kwinana refinery.

Potash project

Minerals exploration

Minerals exploration expenditure for the 2016 financial year was US$175 million, of which US$157 million was expensed. Greenfield minerals exploration is predominantly focused on advancing copper targets within Chile, Peru, Canada and the South-West United States.

Variance analysis relates to the relative performance of BHP Billiton and/or its operations during 2016 financial year compared with the 2015 financial year, unless otherwise noted. Production volumes, sales volumes and capital and exploration expenditure from subsidiaries are reported on a 100 per cent basis; production and sales volumes from equity accounted investments and other operations are reported on a proportionate consolidation basis.

The following footnotes apply to this Operational Review:

The following abbreviations may have been used throughout this report: barrels (bbl); billion cubic feet (bcf); cost and freight (CFR); cost, insurance and freight (CIF); dry metric tonne unit (dmtu); free on board (FOB); grams per tonne (g/t); kilograms per tonne (kg/t); kilometre (km); metre (m); million barrels of oil equivalent (MMboe); million cubic feet per day (MMcf/d); million tonnes (Mt); million tonnes per annum (Mtpa); ounces (oz); pounds (lb); thousand barrels of oil equivalent (Mboe); thousand ounces (koz); thousand standard cubic feet (Mscf); thousand tonnes (kt); thousand tonnes per annum (ktpa); thousand tonnes per day (ktpd); tonnes (t); and wet metric tonnes (wmt).

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PRODUCTION SUMMARY

PRODUCTION SUMMARY

Throughout this report figures in italics indicate that this figure has been adjusted since it was previously reported.

PRODUCTION AND SALES REPORT