Oil prices rose by $1.46 a barrel on Monday, after fresh violence cut production in Nigeria, the world's eighth largest exporter.
Analysts expect the violence to continue for at least a year
Nigeria's oil exports fell by 15% after militants kidnapped nine foreign workers and again attacked facilities in the Niger Delta over the weekend.
With the militia now promising more violence, analysts fear such attacks could continue for at least a year.
The price of Brent crude was up $1.46 to $61.35 a barrel in afternoon trade.
There was no movement to the benchmark US light crude, as the New York Mercantile Exchange is closed on Monday for the US President's Day holiday.
The new surge in violence Nigeria's main oil producing region comes after an earlier attack in January.
The Movement for the Emancipation of the Niger Delta said it would decide the hostages' fate "in the coming days", and has also threatened to start launching rockets at international tankers.
The group is seeking greater control of the oil wealth produced in the region.
"I think this thing [the violence in the Niger Delta] is a chronic situation that will last at least a year," said Tony Nunan, a manager at Mitsubishi Corporation's risk management business.
Anglo-Dutch oil giant Royal Dutch Shell, which has substantial interests in Nigeria, said at the weekend that it had suspended 455,000 barrels per day of production following the latest attacks.