Oil rose above $100 per barrel on Monday amid renewed tensions over Ukraine.
Benchmark U.S. crude for June delivery was up 13 cents to $100.12 a barrel at 0650 GMT in electronic trading on the New York Mercantile Exchange. The contract fell 27 cents to close Friday at $99.99.
Brent crude, a benchmark for international varieties, added 37 cents to $108.26 in London. In the previous session, the contract shed 15 cents to $107.89.
Traders are worried about turmoil in Ukraine and disruption of oil exports from Libya despite muted demand and plentiful supplies.
"The fears are that separatists in Ukraine involving Russian complicity could ratchet up instability in Eastern Europe," said Mizuho Bank in a report.
Pro-Russian insurgents who organized controversial referendums in two regions of eastern Ukraine say about 90 percent of voters have backed their calls for sovereignty. The Ukrainian and Western governments have condemned the balloting as a sham and a violation of international law.
Traders worry Russian energy exports could be interrupted if further instability in Ukraine results in stronger Western sanctions.
In other energy futures trading in New York:
— Wholesale gasoline added 0.8 cent to $2.904 a gallon.
— Heating oil gained 1.1 cents to $2.918 a gallon.
— Natural gas fell 1.2 cents to $4.519 per 1,000 cubic feet.