NEW ORLEANS (AP) — An explosion rocked an offshore oil drilling platform, sending a column of fire into the sky and touching off a frantic search at sea Wednesday for at least 11 reported missing.

Most of the 126 workers on the rig Deepwater Horizon were believed to have escaped safely after the explosion about 10 p.m. Tuesday, Petty Officer Ashley Butler of the Coast Guard public affairs office said.

The rig, more than 50 miles southeast of Venice on Louisiana’s tip, was still burning at midday Wednesday. It was tilting about 70 degrees and threatening to topple into the water. There was no estimate of when the flames might be out.

Helicopters and boats searched the Gulf of Mexico for any sign of the workers who had not been accounted for.

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

The Coast Guard estimated that there were 17 workers evaucated by air and sea Wednesday morning but not all required hospital stays. West Jefferson Hospital in suburban New Orleans said it treated four people, all of whom were released. The University of South Alabama Medical Center said it admitted one person in its burn unit and released five other brought in for evaluation.

The Coast Guard estimated 98 workers were being brought in by boat and were expected ashore Wednesday evening.

When the explosion happened, the rig was drilling but was not in production, according to Greg Panagos, spokesman for its owner, Transocean Ltd. in Houston. The rig was under contract to BP PLC. BP spokesman Darren Beaudo said all BP personnel were safe but he didn’t know how many BP workers had been on the rig.

Panagos said it’s still too early to know what caused the explosion.

“Our focus right now is on taking care of the people,” he said.

O’Berry said Coast Guard environmental teams were on standby in Morgan City, La., to assess any environmental damage once the fire was out.

According to Transocean’s website, the Deepwater Horizon is 396 feet long and 256 feet wide. The semi-submersible rig was built in 2001 by Hyundai Heavy Industries Shipyard in South Korea. The site is known as the Macondo prospect, in 5,000 feet of water.

The rig is designed to operate in water up to 8,000 feet deep and has a maximum drill depth of about 5.5 miles. It can accommodate a crew of up to 130.

A semi-submersible rig is floated to a drilling site. It has pontoons and a column that submerge when flooded with seawater. The rig doesn’t touch the sea floor, but sits low in the water, where it is moored by several large anchors.

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 rig today would run $600 million to $700 million.

Workers typically spend two weeks on the rig at a time, followed by two weeks off. It is equipped with covered lifeboats with supplies to allow them to survive for extended periods if they must evacuate.

Total offshore daily production in the Gulf of Mexico is 1.7 million barrels in federal waters; 6.6 billion cubic feet of natural gas per day is produced in those waters. There are about 35,000 workers offshore in the Gulf at any one time, according to MMS.

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

“In recent years, there’s been a lot more money available and more money spent on training and safety,” he said.

Transocean has 14 rigs working in the Gulf and 140 worldwide. There are 42 deep water rigs either drilling or doing workovers — upgrades and maintenance — in depths of 1,000 feet or greater in the Gulf of Mexico, according to the federal Minerals Management Service.

Since 2001, there have been 69 offshore deaths, 1,349 injuries and 858 fires and explosions in the Gulf, according to the agency, which did not break down the cause of the deaths, the severity of the injuries, or the size of the fires and explosions.


Associated Press Writers Alan Sayre and Mike Kunzelman in New Orleans and Cain Burdeau in Port Fourchon, La., contributed to this report.