"We have evacuated 667 nonessential personnel so far, and we are continuing through the evacuation process as we speak," said ChevronTexaco spokesman Matt Carmichael.

The spokesman said the oil giant was evacuating people from the eastern and central Gulf of Mexico facilities, "but we are watching the track of the hurricane.

Susan Reeves at ExxonMobil said the company "has initiated phase two" in terms of storm preparation, adding "this involves monitoring the storm closely, preparing the structures from wind and rain."

Reeves said "approximately 110 nonessential personnel" were being evacuated from platforms.

"There is no current impact to production operations and there is no production shutting down," she added.

The powerful storm, which has left dozens dead in the Caribbean, appeared headed into the eastern Gulf of Mexico and the Florida panhandle.

Oil giants Shell and BP said Monday they were also evacuating workers from the eastern Gulf of Mexico.

Crude oil prices rose sharply on the shift in Ivan's path. The price of benchmark Brent North Sea crude oil for delivery in October jumped 1.25 dollars to 41.45 dollars a barrel in London.

New York's reference contract, light sweet crude for delivery in October, climbed 1.18 dollars to 43.99 dollars in early deals.