Oil prices rose sharply in Asian trading hours on concerns that separatist tensions in major exporter Nigeria will force further a reduction in supplies.
New York's main contract, light sweet crude for delivery in March, was up $1.07 at $60.95 a barrel from its close of $59.88 Friday in the United States. The New York Mercantile Exchange (Nymex) was closed yesterday for a US public holiday.
In London trade, the price of Brent North Sea crude for April delivery jumped $1.79 to $61.54, off a peak of $61.63.
Separatist guerrillas in Nigeria, Africa's biggest crude producer, threatened further attacks after a weekend of violence forced energy giant Royal Dutch Shell to cut oil exports by a fifth.
The insurgents said the military had abandoned one of its posts in waterways west of the oil city of Warri, allowing the militants to dynamite a floating barrack block and another of Shell's crude oil pipelines. An army spokesman denied that the attack had taken place.
Officials of the oil giant said they had evacuated all oil plants in the immediate area, bringing Nigeria's losses to around 500,000 barrels per day (bpd).
Following the weekend assault, Shell said it was suspending exports from the Forcados terminal, which produces 380,000 bpd and was evacuating an offshore field supplying 115,000 bpd.