Oil prices rose sharply on Thursday, because of the ongoing uncertainty over supplies from Nigeria and Iran.
Analysts expect the Nigerian attacks to continue for some time
At the end of trading, US light crude was up $1.39 to $63.36 a barrel, while London's Brent gained $1.62 to $64.07.
Production in Nigeria has been hit by anti-government militants attacking facilities in the main oil region.
The ongoing stand-off over Iran's nuclear plans unsettles oil prices, as any resulting sanctions by the West could see Tehran limit crude exports.
Although militants in Nigeria's Niger Delta region have released six of the nine foreign oil workers they recently kidnapped, they have pledged to deal "one huge crippling blow to the Nigerian oil industry".
Analysts such as Kevin Norrish of Barclay Capital said the violence in Nigeria had "the potential to get a lot worse".
"It's going to run and run," he said.
In addition to the continuing row over Iran, there is also the threat of attacks on oil facilities in the world's largest producer, Saudi Arabia.
Saudi security forces on Monday killed five suspected militants believed to be planning to attack an oil facility.
The Opec group of oil exporters meets next week to consider changing its current export levels.