Oil prices plunged on Wednesday after government data showed a big, unexpected jump in stockpiles of U.S. crude, compounding pressure as the outlook for global economic growth darkened and the stock market slumped.

U.S. light crude ended Wednesday's session down $2.03 a barrel, or 3 percent, at $65.01, it's lowest closing prices since June 6. The contract hit an eight-week intraday low at $64.51.

Global benchmark Brent crude oil fell $1.68, or 2.3 percent, at $70.78 by 2:26 p.m. ET, after hitting a four-month low at $70.30.

U.S. commercial crude inventories rose by 6.8 million barrels in the week through Aug. 10, the Energy Information Administration reported. Analysts in a Reuters poll had forecast stockpiles would fall by 2.5 million barrels.

The jump in stocks occurred as the nation's crude imports surged by 1 million barrels a day, while its exports fell by more than 250,000 bpd. That offset record activity at American refineries, which ran at 98 percent capacity.

"The imports of crude oil are just remarkable," said John Kilduff, founding partner at energy hedge fund Again Capital. "That we were able to build that much crude oil in inventory in the face of a 98 percent refinery run rate speaks volumes about the burst of supply that hit the market last week."

Stocks at the closely watched U.S. delivery hub at Cushing, Oklahoma rose by 1.6 million barrels. The East and West coasts both saw inventory levels jump by more than 2 million barrels.

Stockpiles of gasoline were down slightly more than expected, while inventories of distillate fuels, including diesel and home heating fuel, rose by 3.6 million barrels, more than three times the increase projected in the Reuters poll.