Huge waves and howling winds from Hurricane Ike damaged several offshore platforms in the Gulf of Mexico, a sign a full recovery of oil and natural gas production in the region could be a long way off.

Threats from hurricanes since late August have already cut more than 20 million barrels of oil supply from the Gulf of Mexico and idled a quarter of the US refinery capacity - digging into supplies and sending gasoline prices up at the pumps.

"There appears to be some long-term damage in the Gulf of Mexico which is going to make a mark on inventories," said Peter Beutel, president of Cameron Hanover in New Canaan, Connecticut.

Chevron Corp. said yesterday that reconnaissance flights revealed several of its platforms in the Gulf of Mexico were toppled by Hurricane Ike, which struck the Texas coast on Saturday in the biggest hit to the oil industry since hurricanes Katrina and Rita in 2005.

"We're unable to say how many or which ones at this time," a spokesman said. "It appears at the moment that they were in the shallower waters along the shelf."

BP, meanwhile, said the drilling derrick on its Mad Dog oil platform in the Gulf of Mexico was toppled.

"Mad Dog's drilling derrick, which sits atop the platform, was toppled and is on the sea bed," the company said. The platform has the capacity to produce up to 100,000 barrels of oil and 60 million cubic feet of natural gas per day.

A BP official said it was too early to say when the platform could resume production or how long the facility's drilling schedule would be delayed.

Despite the damage reports, government officials have said Ike was unlikely to have dealt as big a blow as Katrina and Rita in 2005, which destroyed some 100 rigs.

Shell Oil, the largest oil producer in the Gulf of Mexico, said that initial inspections of its offshore facilities revealed only minor surface damage.

Onshore, 15 refineries representing about 23 per cent of US fuel production capacity remained shut - digging into already-thin US gasoline supplies. The US Department of Energy yesterday said it could be "a week or so" before refineries shut by the hurricanes can restart their operations, but industry sources said it could take much longer before production recovers.

"It will be into October before we are able to start filling in this hole in supplies that was created by these hurricanes," said a source at a major oil company who asked not to be identified.

US gasoline stockpiles are already running at their lowest level since November 2000, and could drop to their lowest on record due to the effects of Ike, according to a Reuters poll of analysts. Gasoline prices have jumped nearly 20 cents since last week to $3.85 a gallon, according to AAA's daily survey.

Energy experts have said that the biggest hurdle for refineries, most of which sustained little damage, could be waiting for power to be restored in areas like Port Arthur, Texas, where Ike hit electricity transmission.

Among the damage reports so far, Shell said its joint-venture refinery in Deer Park, Texas, required some repairs, and ConocoPhillips said its refinery in Belle Chasse, Louisiana - which has been shut since Hurricane Gustav more than two weeks ago - was partly flooded by Ike.

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