U.S crude futures settled down more than 2 percent at a three-month low on Wednesday after the U.S. government reported surprise builds in crude and gasoline inventories.
Prices held their losses after the Federal Reserve announced it would leave interest rate policy unchanged, though the central bank signaled its view of the economy had improved.
The oil and gas stockpile builds came despite the peak summer driving season as refiners cut production amid faltering demand and profits.
U.S. commercial crude in storage rose by 1.7 million barrels to a total of 521.1 million barrels in the week through July 22, the Energy Information Administration said. Analysts had expected a draw of 2.3 million barrels.
Gasoline stocks rose 452,000 barrels, compared with analysts' expectations for a 40,000-barrel increase.