The price of oil has risen to a six-week high as reports of a rescue for debt-laden Greece lifted the euro and helped push the US dollar lower.
A weaker dollar makes oil cheaper for buyers in other currencies. The euro rose 0.3% to $1.3611 in Monday trading.
It had fallen to a nine-month low of $1.3477 on Friday after the US Federal Reserve lifted a key interest rate.
US light, sweet crude oil rose 66 cents to $80.47 a barrel at one point, before falling back to $80.23, up 42 cents.
London Brent climbed 48 cents to $78.67 a barrel.