Oil prices rose as major crude producer Iran and Western powers failed to reach agreement over Tehran's nuclear programme and as the dollar weakened against the euro.
New York's main contract, West Texas Intermediate crude for delivery in July gained 48 cents to $91.34 a barrel.
Brent North Sea crude for July won 82 cents to $107.65 in London deals.
The issue of Tehran's uranium enrichment and stockpile had been at the centre of talks last week between Iran and major world powers - who believe the country's nuclear activities mask a push to build atomic weapons.
Iran, already under heavy sanctions for refusing to suspend its nuclear programme, has denied the accusations and threatened to disrupt Middle East oil supply if it is faced with further sanctions.
Traders said that oil prices were also supported by a weaker greenback, which makes dollar-denominated crude cheaper for holders of other currencies, boosting demand and in turn prices. The euro rose versus the dollar after opinion polls indicated a victory for pro-austerity conservatives in an upcoming Greek general election.
The New Democracy party, which backs a deal with the European Union and International Monetary Fund, is tipped to secure most seats in the June 17 general elections but without an outright majority, opinion polls showed yesterday.
