Instability in Nigeria, the fifth largest OPEC producer, has pushed US crude oil futures past the key $50 a barrel level. It was for the first time that oil breached the $50 level.

US light crude futures rose 86 cents a barrel to $49.74, breaking the previous record of $49.40 set over a month ago. Brent crude surged 87 cents to a new high of $46.25.

With the rebels announcing the beginning of a new offensive, against the government from the end of this week, across Nigeria's entire southern delta region, oil group Royal Dutch/Shell announced on Monday that it was pulling some staff out of the impoverished area.

Stating that overseas oil majors are collaborating with the government of President Olusegun Obasanjo in acts of genocide, the rebels have ordered the oil companies to stop production by October 1.

Uncertainty over supplies from Yukos, Russia's top exporter; Saudi Arabia, where clashes between security forces and suspected al Qaeda followers continue to rage, and Iraq where pipelines are frequent target of saboteurs, is also adding to oil woes.

Besides, the Hurricane Ivan also damaged petroleum facilities in the United States, which led to delayed oil shipments.