Transocean Ltd.

Transocean Ltd. is an offshore drilling contractor domiciled in Steinhausen, Switzerland, the world's largest offshore drilling company by revenue, operating a fleet of drillships and semi-submersible rigs that drill oil and gas wells for oil companies in deep water around the world. The company traces its history to an American drilling contractor founded in the 1950s and grew over subsequent decades through a long series of mergers with other drilling companies before relocating its corporate domicile to Switzerland in 2008. Transocean owned and operated the Deepwater Horizon, the drilling rig leased to BP that exploded in the Gulf of Mexico in 2010, causing the largest marine oil spill in United States history, an event that led to major changes in offshore drilling safety regulation and significant liabilities for the company.