LA NOUVELLE-ORLEANS - Les autorités de Louisiane tentaient vendredi d'éviter une marée noire dans les eaux du Golfe du Mexique, qui menacerait un écosystème fragile, alors que les recherches se poursuivaient pour retrouver onze employés toujours portés disparus.

Le pétrole a apparemment cessé de fuir de la plate-forme pétrolière qui a sombré jeudi matin au large des côtes de Louisiane, après avoir brûlé pendant 36 heures, selon les autorités.

L'incendie a été éteint, mais les autorités craignaient dans un premier temps que jusqu'à 1,27 million de litres de pétrole brut s'échappe chaque jour de la plate-forme reposant à 1.524 mètres sous l'eau.

Le contre-amiral Mary Landry, des garde-côtes, a affirmé que ses équipes surveillaient de très près la plate-forme pétrolière pour éviter des risques de fuite sous-marine.

Le groupe pétrolier britannique BP, qui exploitait la plate-forme pétrolière et dirige les opérations de nettoyage, a fait savoir vendredi qu'il avait engagé des moyens importants pour lutter contre la pollution.

Cent onze employés qui se trouvaient sur la plate-forme ont été ramenés à terre, dont 17 qui ont été hospitalisés. Quatre se trouvaient dans un état critique vendredi.

NEW ORLEANS – Rescuers in helicopters and boats searched the Gulf of Mexico for 11 missing workers Wednesday after a thunderous explosion rocked a huge oil drilling platform and lit up the night sky with a pillar of flame. Seventeen people were injured, four critically.

The blast Tuesday night aboard the Deepwater Horizon rig 50 miles off the Louisiana coast could prove to be one of the nation's deadliest offshore drilling accidents of the past half-century.

The Coast Guard held out hope that the missing workers escaped in one of the platform's covered lifeboats.

Nearly 24 hours after the explosion, the roughly 400-by-250-foot rig continued to burn, and authorities could not say when the flames might die out. A column of boiling black smoke rose hundreds of feet over the Gulf of Mexico as fireboats shot streams of water at the blaze.

"We're hoping everyone's in a life raft," Coast Guard Senior Chief Petty Officer Mike O'Berry said.

Adrian Rose, vice president of rig owner Transocean Ltd., said the explosion appeared to be a blowout, in which natural gas or oil forces its way up a well pipe and smashes the equipment. But precisely what went wrong was under investigation.

Crews were doing routine work before the explosion and there were no signs of trouble, Rose said.

A total of 126 workers were aboard the rig when it blew up. The Coast Guard said 17 were taken by air or sea to hospitals. Four were reported in critical condition. Others suffered burns, broken legs and smoke inhalation.

Nearly 100 other workers made it aboard a supply boat and were expected to reach the Louisiana shore by evening.

Kelly Eugene waited with nine family members for husband Kevin Eugene, 46, a cook on the Deepwater Horizon. A catering company operating on the rig notified her he was safe.

"He's on the boat. That's all we know. And that's all we need to know," she said.

The rig was tilting as much as 10 degrees after the blast, but earlier fears that it might topple over appeared unfounded. Coast Guard environmental teams were on standby, though officials said the damage to the environment appeared minimal so far.

The rig, which was under contract to the oil giant BP, was doing exploratory drilling but was not in production, Transocean spokesman Greg Panagos said. Seventy-nine Transocean workers, six BP employees and 41 contract workers were aboard.

Ted Bourgoyne, a retired professor of petroleum engineering at Louisiana State University, said the explosion was probably caused by natural gas or a mixture of oil and gas coming up through the well, combined with some kind of ignition source.

He said there are numerous defenses on a modern rig to prevent something like that from happening. For instance, fluids used in drilling are weighted with barium sulfite to prevent gas from traveling up the well, and there are alarms to alert workers to gas. Machinery is built to prevent sparking and is placed as far away as possible from places where gas might leak.

"In almost all of these things, there's not one thing that happens; it's a series of things," Bourgoyne said.

Rose said the crew had drilled the well to its final depth, more than 18,000 feet, and was cementing the steel casing at the time of the explosion.

"They did not have a lot of time to evacuate. This would have happened very rapidly," he said.

According to Transocean's website, the Deepwater Horizon is about twice the size of a football field. Built in 2001 in South Korea, it is designed to operate in water up to 8,000 feet deep, drill 5 1/2 miles down, and accommodate a crew of 130. It floats on pontoons and is moored to the sea floor by several large anchors.

The site of the accident is known as the Macondo prospect, in 5,000 feet of water.

Workers typically spend two weeks on the rig at a time, followed by two weeks off. Offshore oil workers are typically well paid, earning $40,000 to $60,000 a year — more if they have special skills.

Last September, the Deepwater Horizon set a world deepwater record when it drilled down just over 35,000 feet at another BP site in the Gulf of Mexico, Panagos said.

"It's one of the more advanced rigs out there," he said. Panagos did not know how much the rig cost to build but said a similar one today would run $600 million to $700 million.

Kelly Eugene said her husband flew to work on the rig, and until Tuesday's explosion, that was the part of his job that scared her most. Kevin Eugene has worked in the offshore industry about 12 years and had been on the Deepwater Horizon about a month. Until now, she said, hurricane evacuations were the worst he had been through.

"My biggest fear is the helicopter ride," she said.

Working on offshore oil rigs is a dangerous job but has become safer in recent years thanks to improved training, safety systems and maintenance, said Joe Hurt, regional vice president for the International Association of Drilling Contractors.

Since 2001, there have been 69 offshore deaths, 1,349 injuries and 858 fires and explosions in the Gulf, according to the federal Minerals Management Service.

There are 42 rigs either drilling or doing upgrades and maintenance in depths of 1,000 feet or greater in the Gulf of Mexico, according to the agency. They employ an estimated 35,000 people. Transocean has 14 rigs in the Gulf and 140 worldwide.

In 1964, a catamaran-type drilling barge operated by Pan American Petroleum Corp. near Eugene Island, about 80 miles off Louisiana in the Gulf of Mexico, suffered a blowout and explosion while drilling a well. Twenty-one crew members died.

The deadliest offshore drilling accident took place in 1988, when an Occidental Petroleum platform about 120 miles off Aberdeen, Scotland, was rocked by explosions and fire. A total of 167 men were killed.