"To protect its rights, Transocean also filed cross-claims against BP entities and other parties involved in the Macondo well incident to enforce its indemnification rights," the group said in a statement.
Transocean operated the Deepwater Horizon rig which exploded on April 20, 2010, killing 11 workers and causing millions of gallons of oil to pour into the Gulf of Mexico.
But it claimed that in the drilling contract for the rig, BP had agreed to "assume full responsibility for and defend, release and indemnify Transocean from any loss, expense, claim, fine, penalty or liability for pollution or contamination, including control and removal thereof, arising out of or connected with operations under the contract.
"Transocean expects BP to honour its contractual indemnification obligations under the contract," it added.
Earlier Thursday, BP announced that it has sued Transocean for damages of $40 billion (27 billion euros) over the disaster.
The British oil giant filed its suit against Swiss-based Transocean in a New Orleans court on Wednesday, the one-year anniversary of the start of the biggest maritime oil spill in US history.