Mining giant BHP Billiton Wednesday reported that iron ore production in resource-rich Western Australia saw another record in the six months to December, while petroleum output was on track. After commodity price volatility in 2012, which prompted miners to shelve some expansions, BHP said iron ore production for the half year was 81.962 million tonnes, a 2.0 percent jump year on year. \"Western Australian Iron Ore delivered a 12th consecutive December half year production and sales record as the business continued to benefit from the company\'s decade-long investment in supply chain capacity,\" it said. Melbourne-based BHP said it was on track for Western Australia production of iron ore -- keenly sought by China -- to increase by five percent to about 183 million tonnes in the 2013 financial year. In petroleum, expected to account for a greater amount of revenue in coming years, the company produced 121 million barrels of oil equivalent during the December half, an 11 percent increase from same period in the previous year. Full year guidance was unchanged at 240 million barrels of oil equivalent. In its half-year production report, the world\'s biggest diversified miner also said it expected a \"substantial reduction\" in unit costs at Queensland coal operations after it closed an unprofitable mine in that state. BHP\'s production of metallurgical coal, used in steel-making, climbed five percent in the December quarter over the December 2011 quarter. \"At the end of the December 2012 quarter, Queensland Coal production was approaching full supply chain capacity,\" BHP said. \"The associated increase in productivity, broader economies of scale and the closure of high cost capacity is expected to deliver a substantial reduction in unit costs in the second half of the 2013 financial year.\" Copper output was also strong, jumping five percent over the quarter compared to the December 2011 quarter, but aluminium production fell five percent and nickel was down 10 percent on the same measure.