U.S. crude inventories rose 1.4 million barrels last week, compared with analysts' expectations for a decrease of 1.4 million barrels, the Energy Information Administration reported.
Gasoline stocks slumped by 3.3 million barrels, compared with forecasts for a 200,000-barrel drop, according to Reuters.
U.S. West Texas Intermediate (WTI) crude CLc1 was up 70 cents at $40.21 a barrel by 10:55 a.m. EDT (1555 GMT). On Tuesday, it settled below $40 a barrel the first time since April.
Brent crude LCOc1 rose 62 cents to $42.42. It hit a more than three-month low of $41.51 in the previous day.
"With spot prices getting under $40 yesterday, we are not surprised to see spot prices rebounding on the gasoline draw. But I think this will be shortlived," said Tariq Zahir, trader in crude oil spreads at Tyche Capital Advisors in New York.
"The bottom line is the Street in the second quarter got a little ahead of itself in calling for rebalancing of supply-demand after Canadian and Nigerian supply disruptions. We are going into the third and fourth quarters with those supplies back online and refinery maintenance coming up."