Benchmark West Texas Intermediate crude for September delivery lost $1.50 to $98.09 per barrel Wednesday morning on the New York Mercantile Exchange. In London, Brent crude fell 59.8 cents to $117.69 per barrel on the ICE Futures exchange.
The Energy Department says oil inventories rose 2.3 million barrels to 354 million barrels last week. Gasoline supplies increased by 1 million barrels to 213.5 million barrels. Gasoline demand over the last four weeks remains below year-ago levels.
Gasoline pump prices rose about half a cent on Wednesday to a national average of $3.698 a gallon. That's nearly $1 more than a year ago.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
Oil prices fell below $99 a barrel Wednesday in Europe after a report showed U.S. crude supplies unexpectedly jumped last week, suggesting demand may be weakening.
By early afternoon in Europe, benchmark oil for September delivery was down 73 cents to $98.86 a barrel in electronic trading on the New York Mercantile Exchange. Crude rose 39 cents to settle at $99.59 on Tuesday.
In London, Brent crude fell 60 cents to $117.68 per barrel on the ICE Futures exchange.
The American Petroleum Institute said late Tuesday that crude inventories rose 4.0 million barrels last week while analysts surveyed by Platts, the energy information arm of McGraw-Hill Cos., had predicted a drop of 2.3 million barrels.
Inventories of gasoline dropped 600,000 barrels last week while distillates rose 2.9 million barrels, the API said.
The Energy Department's Energy Information Administration reports its weekly supply data -- the market benchmark -- later Wednesday.
Investors are also closely watching negotiations among U.S. leaders to raise the government's debt limit and Europe's bid to contain its own debt crisis.
"There is no doubt that U.S. recovery to date has been extremely fragile," said Richard Soultanian of NUS Consulting. "The uncertainty created by each of these challenges, at best, could derail the nascent economic recovery and, at worst, plunge us back into recession."
During the past days, the dollar has been weakening on back of a potential U.S. default. That has helped boost oil prices by making crude cheaper for investors holding other currencies.
On Wednesday, however, the euro slipped to $1.4475 from $1.4518 on Tuesday.
"Oil is no longer gaining anything from the U.S. dollar's continuing slide," said analysts at Commerzbank in Frankfurt. "These prices reflect concerns that the conflict over how to handle the U.S. debt limit and the threat of a de facto bankruptcy could hit demand in the world's biggest oil consuming country."
In other Nymex trading in September contracts, heating oil fell 1.51 cents to $3.11 a gallon while gasoline lost 0.67 cent to $3.0918 a gallon. Natural gas futures rose 3.1 cents to $4.362 per 1,000 cubic feet.
Alex Kennedy in Singapore contributed to this report.