Fears of a major oil spill in the Gulf of Mexico have increased after an oil drilling rig that had burnt for 36 hours sank.
The fire went out as the Deepwater Horizon, operated by Transocean Ltd, sank below the surface about 68km off the Louisiana coast.
The rig was drilling BP Plc's Macondo project with 126 workers on board when it was ripped by an explosion and fire on Tuesday night. Some 115 workers escaped, including 17 helicoptered to New Orleans area hospitals with injuries.
Search and rescue operations turned up two empty lifeboats, and officials cited dim hopes that the 11 workers missing since the explosion about on Tuesday night would be rescued.
"We do continue with search and rescue activities," Coast Guard Commander Rear Admiral Mary Landry said. "As time passes, however, the probability of success in locating the 11 missing persons decreases."
Transocean, based in Zug, Switzerland and the world's largest offshore drilling contractor, said some of the missing may not have been able to escape the rig.
"Based on reports of crew members, at the time of the incident, they believe they may have been on board and not able to evacuate," said Transocean vice president Adrian Rose.
The explosion comes almost three weeks after President Barack Obama unveiled plans for a limited expansion of US offshore oil and gas drilling.
It was unclear whether the rig sank to the bottom in about 1,500 metres of water, or how much oil still flowed or had spilt from the well, officials said. By yesterday afternoon, a long oil slick extended from the site, which has the potential to be a "major" oil spill, the Coast Guard said.
Officials said floating oil spill barriers, skimmers and airplanes to drop dispersant were being prepared to control and clean up the spill. A remotely operated unmanned submarine, commonly used in the industry, was deployed to determine the exact location and condition of the rig and the situation of the well.
Officials said an investigation had begun to determine exactly what happened. Sometimes oil and gas well drilling hits pockets of high pressure that were not anticipated and cannot be controlled, experts said.
The well in Tuesday's incident was the first of a series to be drilled and was in the process of being temporarily plugged pending production.
The rig explosion did not have an effect on crude oil prices because the well was not in production mode.
Reuters