Factbox: Companies involved in the Gulf rig accident

(Reuters) - The explosion aboard the Deepwater Horizon floating drilling rig in the U.S. Gulf of Mexico offshore Louisiana on April 20 resulted the presumed death of 11 workers. The rig sank, and crude oil has been gushing from the sea floor, threatening coastal wildlife and commercial fishing. The following companies owned, operated or provided services to the drilling rig:

Transocean Ltd - The Zug, Switzerland-based company owned and operated the Deepwater Horizon Rig. The rig went into service in 2001 and was drilling the Macondo prospect about 40 miles off the coast of Louisiana.

BP Plc - BP hired Transocean's rig at a rate of about $500,000 per day to drill the well. BP is the project's operator and has a 65 percent working interest in the well.

Anadarko Petroleum Corp - The Houston company owns a 25 percent nonoperating interest in the well.

Cameron International Corp - The Houston company supplied a piece of equipment known as a blowout preventer. Blowout preventers are put in place to stop an uncontrolled flow of oil or gas. The Deepwater Horizon's blowout preventer failed to operate and seal the well.

Halliburton Co - The oilfield services company, which has headquarters in Dubai and Houston, provided a number of services on the Deepwater Horizon. The company was providing cementing on the well to stabilize its walls, according to Transocean's website.

(Reporting by Anna Driver in Houston; Editing by Lisa Von Ahn)