The price of certain grades of oil - including the UK's Brent crude - has jumped amid political protests in the Middle East.
Brent rose by $3.36 (£2.09) a barrel to $104.30 (£65.07) for April delivery, its highest since September 2008.
The US benchmark oil, West Texas Intermediate (WTI) rose by a far smaller 25 cents to $85.84 a barrel.
The gap between the two prices has been at record levels recently, partly because stocks of WTI are high.
Seasonal maintenance of some refineries is also causing spikes in certain grades of crude oil.
There is concern that the recent toppling of regimes in Tunisia and Egypt is prompting further instability in the Middle East and North Africa, which together account for more than a third of the world's oil.
Protests have also taken place in Yemen, Algeria and Iran.
Christopher Bellew, a broker at London's Bache Commodities said: "We're staying up because of the continued risk of further unrest in the Middle East."