Markets were also supported by signs Greeks would elect a pro-austerity government in upcoming polls.
This eased concerns the debt-wracked country would exit the euro zone and trigger a global economic crisis.
New York's main contract was up 89 cents to $91.75 a barrel while Brent crude gained 68 cents to $107.51.
On Saturday the head of Iran's Atomic Energy Organisation said Tehran had "no reason" to suspend its enrichment of uranium to 20%.
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.
Analaysts said that Iran is desperate for oil revenues to return and was hoping its more accommodating attitude would see oil supply bans lifted immediately.
Prices were also lifted by a slight easing of bearish sentiment over the euro zone's debt troubles, analysts said.
Opinion polls published on Sunday showed Greek pro-bailout conservative party New Democracy is expected to secure most seats in the June 17 general elections but without an outright majority. Such a result would be welcomed by investors who feared that radical left party Syriza - which rejects austerity measures outright - would sweep into power.
