BP’s partner in the Deepwater Horizon disaster has blamed them for the majority of the failures that preceding the oil spill.

Now estranged from BP, it was Transoceant that owned the rig, also supplying most of the personnel. The lawsuit brought by BP is valued $40 billion (£24.8 billion).

After holding its own internal investigation, Transocean decided to plug the well using cementing techniques that are not approved in the USA. It claims that BP misinterpreted critical pressure tests for the well, and missed vital warning signs of a possible blowout. Their report states that the force of the gushing oil stopped the blowout preventer from sealing the well. BP stands accused of using a faulty well design.

BP said yesterday that the Transocean report “fails to acknowledge the significance of Transocean’s role in the event.”