BHP Billiton has beaten its iron ore export guidance for the 2015 financial year, and vowed to grow exports of the bulk commodity by seven per cent over the next 12 months.

The miner had promised to export 250 million tonnes from its Pilbara operations, including tonnes owned by joint venture partners, and went beyond that to ship 256 million tonnes.

BHP's share of those exports was 233 million tonnes, which was also higher than the 230 million tonnes forecast.

Global iron ore supplies are expected to boom over the next 12 months, as established players continue to grow exports and as new producers like Gina Rinehart's Roy Hill come into first production.

BHP's Pilbara system is expected to ship 270 million tonnes (including those owned by joint venture partners) over the next 12 months, and BHP's share of those tonnes is expected to rise from 233 million tonnes to 247 million tonnes.

BHP's long term goal is to be capable of exporting 290 million tonnes of iron ore from its Pilbara system, including tonnes owned by joint venture partners, each year by June 2017.

The benchmark iron ore price averaged $US71.67 during the year to June 30, 2015, and was fetching $52.10 on Wednesday.

BHP's copper guidance had already been downgraded in April to 1.7 million tonnes, and the miner achieved the revised target.

Despite the petroleum division having to adapt to an era of lower oil and gas prices, the division still narrowly beat guidance of 255 million barrels of oil equivalent, with the company delivering 256 million barrels of oil equivalent.

BHP announced last week that it would wear more than $US2 billion of impairments on its US shale division, and it confirmed up to $US650 million of further impairments on redundancies and certain copper projects.

The demerger of South32 was completed during the June quarter and BHP will record a net loss on the transaction of $US2.1 billion.

BHP's Australian shares last traded at $26.82.