New York's main contract, light sweet crude for delivery in April, gained one dollar to $80.68 a barrel.
London's Brent North Sea crude for April climbed 84 cents to $79.02.
The euro shot up against the dollar Wednesday after Greece announced tough new austerity measures that analysts said opened the door to concrete assistance from the country's European partners.
The single European currency at one point jumped to a two-week high of 1.3729 dollars after Athens unveiled tax hikes and spending cuts.
A weak dollar boosts dollar-priced crude oil because it becomes cheaper for buyers using stronger currencies, which in turn tends to lift demand.
The pan-European FTSEurofirst 300 index of top shares ended 0.8 percent higher at 1,035.56 points, its highest close since Jan 21, helped by Standard Chartered's report of record profits for 2009.
Shortly after midday the Dow Jones Industrial Average was up 31.44 points, or 0.30 percent, at 10,437.42. The Standard & Poor's 500 Index was up 4.92 points, or 0.44 percent, at 1,123.23. The Nasdaq Composite Index was up 7.12 points, or 0.31 percent, at 2,287.91.
Gold rose to a 6-1/2-week high at $1,141.70 an ounce as the dollar extended losses and as broader fears over the outlook for paper currencies lent further support to the precious metal.
