British oil group BP and US rivals ConocoPhillips and Shell on Thursday evacuated workers from their energy installations in the Gulf of Mexico, as Tropical Storm Gustav loomed.

"We're completing the evacuation of non-essential personnel from offshore platforms," BP said in an automated phone message. "Production is not impacted by the storm."

ConocoPhilips said it was evacuating 44 people Thursday from its Magnolia platform and was prepared to remove its remaining personnel Friday and Saturday if the storm continued on its projected track.

"Similar preparations have begun on the South Louisiana Inland Water asset (SELA) operations," ConocoPhillips said.

Shell said it was evacuating about 300 personnel, after removing almost 400 people Wednesday.

"We expect to evacuate the remaining 600 personnel on Friday and Saturday," it said.

Gustav, which was threatening to regain hurricane strength, was expected to enter the Gulf of Mexico over the weekend, then make landfall in Louisiana and Texas on Monday, according to the National Hurricane Center.

About a quarter of US crude oil installations are located in the Gulf of Mexico.

ExxonMobil said it was preparing for the storm and "identifying personnel for possible evacuation to shore."

The threat of Gustav raised grim memories of the 2005 hurricanes Katrina and Rita that damaged or destroyed about 165 oil platforms of the some 4,000 located in the Gulf.

According to oil industry analyst Andy Lipow, based in Houston, Texas, Gustav could interrupt 75 percent of the Gulf's crude oil production, or more than one million barrels per day.

"Everyone is comparing Gustav to Hurricane Katrina that hit three years ago," Lipow said.

"We'll have a supply disruption, but how quickly can the industry recover is going to be the key," he said.

Lipow said the oil industry presently was better girded for storms.

"This time the oil and gas industry is much better prepared, not only on offshore facilities but on onshore facilities."