Agence France-Presse: Transocean, which owns the BP-leased offshore rig gushing oil into the Gulf of Mexico, filed a petition in a US court Thursday to limit its liability in the spill to 27 million dollars. While British energy giant BP is responsible for the cost of the cleanup, BP executives told a congressional hearing Tuesday that Transocean was responsible for the failure of a key giant valve system. Transocean chief executive Steven Newman passed the buck back, saying: "All offshore oil and …