BP is suing Transocean for at least $40 billion in damages, accusing the rig owner of causing last year's deadly blowout in the Gulf of Mexico that led to the worst offshore oil spill in U.S. history.
The British oil giant also is suing the maker of the device that failed to stop the calamitous oil spill.
The developments came in separate court filings in federal court in New Orleans on Wednesday, the one-year anniversary of the disaster.
BP says every single safety system and device and well control procedure on the Deepwater Horizon rig failed. It also says Cameron International provided a blowout preventer with a faulty design.
Eleven people were killed when the rig exploded on April 20, 2010, leading to more than 200 million gallons of oil spewing from an undersea well.