The price of certain grades of oil has jumped amid political protests in the Middle East.
Brent crude rose on Monday by $US3.36 per barrel to $US104.30 p/b for April delivery, its highest since September 2008.
West Texas Intermediate rose by 25 cents to $US85.84 per 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.
The BBC reports there is concern that the recent toppling of regimes in Tunisia and Egypt could lead to 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.