New York's main contract, West Texas Intermediate (WTI) for April delivery, fell 33 cents to USD 101.12 in mid-morning trade, while Brent North Sea crude for April rose 20 cents to USD 107.96.
Kenny Kan, market analyst at CMC Markets in Singapore, said an increase in weekly crude inventories in the United States weighed on WTI prices.
A rise in stockpiles indicates weaker demand in the world's biggest oil consuming nation.
"Many analysts considered the data to be bearish," Kan told AFP.
The US Department of Energy said commercial crude-oil inventories rose 1.4 million barrels in the week ending February 28, more than analysts' consensus estimate of a 1.0 million barrel gain.
Investors are also keeping an eye on developments in Ukraine after Russian-backed troops moved into Crimea, sparking the worst crisis in Europe since the Cold War.
Russia vies with Saudi Arabia as the world's largest crude oil producer, and is the second-largest producer of natural gas.
More than 70 per cent of its gas and oil exports to Europe pass through Ukraine, and analysts fear that an escalation of the crisis could lead to a disruption in supplies.