New York's main contract, light sweet crude for delivery in December, rose eight cents to $87.48 a barrel.
Brent North Sea crude for December delivery gained 40 cents to $109.96.
Traders were cheered by comments from European leaders after a weekend summit convened to hammer out a plan to tackle the eurozone debt crisis, said Jonathan Barratt, managing director of Commodity Broking Services in Sydney.
"We're still waiting for an outcome... But there's optimism that the outcome will be positive," he told AFP.
"Given the way equities markets have reacted (to the talks), there's more optimism out there which will result in more demand for crude."
Major Asian bourses, including those in Hong Kong, Japan and Australia opened higher in early trade, lifted by positive remarks by European leaders emerging from the summit in Brussels.
Officials including IMF chief Christine Lagarde hailed the "good progress" made at at the talks aimed at overcoming a crisis that has threatened to pitch the world into a fresh recession.
Notably, French President Nicolas Sarkozy and German Chancellor Angela Merkel seemed to have resolved previous differences over boosting the EU bailout fund, telling reporters there was "a quite broad agreement" on the main sticking point.