The Department of Energy said commercial inventories fell by 900,000 barrels in the week ending June 10, far fewer than the 2.33 million predicted in a Bloomberg survey, suggesting demand is easing in the world's top oil consumer.
The news sent the commodity tumbling and at about 0320 GMT today in Asia US benchmark West Texas Intermediate slipped 46 cents, or 0.96 per cent, to USD 47.55 while Brent shed 34 cents, or 0.69 per cent, to USD 48.63.
Supply-side fears have increased, with Canada's output likely to normalise as wildfires that hit its oil region subside while Nigerian rebels, who have been attacking crude installations, consider peace talks with the government.
"We still, when you think about it, have a surplus of supply because it has really only been disruptions that have seen that surplus disappear," David Lennox, an analyst at Fat Prophets in Sydney, told Bloomberg News.
He added: "The market is now starting to suggest that once the disruptions are behind us, surplus will re-appear and the rally that we have seen in the prices will evaporate."
Federal Reserve boss Janet Yellen on Wednesday sounded a warning about the possible impact of a "Leave" vote as the US central bank lowered its economic growth and interest rate projections over the next few years.
A Bank of Japan decision to hold steady on monetary policy despite the weak economy has also added to uncertainty, said CMC Markets analyst Margaret Yang.
