BP claims Transocean is guilty of negligence, on the grounds that 'every single safety system and device and well control procedure on the Deepwater Horizon failed'. Not surprisingly, Transocean slammed the suit as 'specious and unconscionable', a 'desperate bid' by BP to abrogate responsibility (which obviously it would never do). BP is also demanding that Cameron be forced to cough up 'all or part' of BP's costs, because its blowout preventer 'failed to work' and was 'flawed in design'. Both suits have been filed in New Orleans, and the timing is because yesterday marked the deadline for the parties involved to sue each other.
The stakes are pretty high here. BP has already set aside $41bn to cover the fall-out, including a $20bn compensation pot that it's handed over to the US authorities. But ratings agency Moody's said this week that the final figure could be closer to $60bn - it points out that BP hasn't really budgeted for the costs of paying any fines yet (apart from those under the Clean Water Act). Moody's reckons BP could actually afford this, if push came to shove (it's already selling $30bn of assets, and has a similar amount of cash in the bank, plus more assets that could be sold if needs be). But anything it can do to spread the burden would obviously be a huge bonus.
The question is, will BP be able to convince the US courts that Transocean and Cameron deserve some of the blame? BP remains massively unpopular in the US - but it might actually be helped by the official White House report, which seemed to spread the blame around all those involved. For what it's worth, Moody's reckons Cameron will get away largely unscathed, but Transocean will find it harder to dodge the bullet. Either way we can now expect an extended period of legal wrangling; BP may not know what the real damage is until the back end of next year. Good news for the lawyers, if nobody else.