The investigation into the oil spill in the Gulf of Mexico is expected to turn to the Marshall Islands where the rig was registered.
Under international law, offshore rigs like the Horizon are treated as ships and it has been suggested the Marshall Islands is more culpable than the United States because the Deeptwater Horizon rig carried its flag.
Our correspondent, Giff Johnson, says the Marshalls operates the third largest ship registry, with more than 2,000 vessels flying its flag.
He says investigators have the Marshall Islands in their sight.
"Probably it's only a matter of time before the Marshall Islands is tagged on to those suits. But as far as I know at the moment, the Marshall Islands hasn't been brought into any of the legal actions. I know also that the US Justice Deparment has launched a criminal investigation into the whole matter."
The Deeptwater Horizon rig exploded in April killing more than 10 platform workers and injuring 17 others and has since gushed crude oil into the sea.