Global oil supply is growing at a “breakneck speed” despite a collapse in prices, the world’s leading energy body said on Wednesday, with the glut likely to persist well into 2016 even as demand increases at its fastest pace in five years. The International Energy Agency, the west’s oil watchdog, said global oil supplies outstripped demand in the second quarter by 3m barrels a day, the most since 1998, even as it raised its forecast for demand this year and next. “While a rebalancing has clearly begun, the process is likely to be prolonged,” the IEA said in its closely watched monthly oil market report. A supply overhang it expects to persist next year suggests “global inventories will pile up further”. Even so, global oil supply fell by 600,000 barrels a day in July to 96.6m b/d, the IEA said, largely on slowing non-Opec output. While production growth from countries such as the US has shrunk from 2014 highs, it is still running at around 1.2m b/d so far this year “thanks to hefty investment made previously”, the agency said.