Global oil prices pushed modestly higher Friday on tensions in Ukraine, but gains were tempered by the dollar's continued strength.
New York's main contract, West Texas Intermediate (WTI) for delivery in April delivery, added 56 cents from Thursday's close to $99.46 a barrel.
Brent North Sea crude for May gained 47 cents to $106.92 per barrel.
"The oil market is being driven higher by increased fears of a disruption in crude supplies following the expansion of US sanctions against Russia," said analysts at London-based brokerage PVM.
Traders were closely monitoring events in eastern Europe after the United States and European Union announced fresh sanctions on Moscow Thursday over the annexation of Crimea.
US sanctions took aim at a key figure in Russia's oil and gas industry, Geneva-based billionaire trader Gennady Timchenko, whose Gunvor firm handles much of Russia's energy exports.
"Gunvor is one of the world’s largest commodity traders," CMC Markets Singapore said in a market commentary.
"Russian President Vladimir Putin is rumored to have investments in the company and direct links to Timchenko's energy activities," it said.
Gunvor denied the Putin links and said Timchenko had sold his shares to a partner ahead of the sanctions, ostensibly keeping Gunvor itself outside sanctions enforcement.
But Washington's move made clear that the energy industry could be impacted by the rising tensions.
Russia provides about a quarter of Europe's natural gas supplies, with a significant portion of that flowing through pipelines that cross Ukraine.
Traders fear that an escalation of the crisis would disrupt those supplies.
The dollar remained higher after its jump Wednesday on Federal Reserve Chair Janet Yellen's remarks that suggested to some an interest rate hike would come early next year.
With crude priced in dollars, a strengthening of the unit makes the commodity more expensive, dampening demand and prices.