New York's main contract, West Texas Intermediate crude for delivery in February, gained five cents to $100.44 a barrel in morning trade.
Brent North Sea crude for March delivery was down six cents to $114.49.
"It is mainly the oil inventory data that is affecting crude prices," said Ker Chung Yang, commodity analyst at Phillip Futures in Singapore.
The US government's weekly oil inventory report showed a fall in crude stocks that was explained by a slowdown in imports and mounting stockpiles of refined products due to slower demand.
The report also said petrol use in the world's second largest energy consumer had dropped to 8 million barrels a day last week, the lowest level since September 2001.
The European Union's failure to agree on setting an embargo on Iranian oil also eased pressure on the market, analysts said.
EU nations Thursday agreed to sanction Iran's central bank and freeze assets used to finance its nuclear programme, but have yet to reach an oil embargo deal that could penalise debt-hit Greece.
The financially stressed nation imports 34.2 percent of its oil from Tehran, and is seeking up to a year to phase out existing contracts. Some countries, including Britain, France and Germany, want a three-month deadline.
The embargo will now be finalised when the bloc's foreign ministers meet on Monday.
The new EU sanctions are part of a concerted effort with the United States to pressure Iran into halting its controversial nuclear activities, which the West suspects are aimed at developing nuclear weapons.
Iran says its nuclear programme is purely for civilian use.