(CNN) -- Transocean Deepwater Inc. will pay the second-largest environmental fine in U.S. history for its role in the deadly 2010 Deepwater Horizon explosion and spill in the Gulf of Mexico, the Justice Department said Thursday.
The company was sentenced to pay $400 million and other penalties after it pleaded guilty in a Louisiana federal court Thursday to violating the Clean Water Act by its illegal conduct leading to the disaster, Attorney General Eric Holder said.
Eleven workers were killed when the Transocean oil rig exploded. The blast and ensuing fire damaged the rig, causing 4.9 million barrels of oil to spill into the Gulf, according to a 2011 report by the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling.
The nation's largest environmental crime penalty was the $4 billion paid by BP Exploration and Production Inc. for its role in the disaster, federal authorities said. BP contracted Transocean to do the drilling and had BP officials on the rig.
"Transocean's guilty plea and sentencing are the latest steps in the department's ongoing efforts to seek justice on behalf of the victims of the Deepwater Horizon disaster," said Holder.
Most of the $400 million will be used to restore and rebuild the Gulf coast region, authorities said.
"The Deepwater Horizon explosion was a senseless tragedy that could have been avoided," Assistant Attorney General Lanny A. Breuer said in a statement. "With today's guilty plea, BP and Transocean have now both been held criminally accountable for their roles in this disaster."
U.S. District Judge Jane Triche Milazzo of the Eastern District of Louisiana accepted Transocean's guilty plea, which it agreed to in a deal with the government in January.
In its plea, Transocean admitted that its crew on the Deepwater Horizon rig was acting at the direction of BP's well site leaders and were "negligent in failing to investigate fully clear indications that the Macondo well was not secure and that oil and gas were flowing into the well," the Justice Department said.
The Macondo well was the source of the oil spill.
Under the plea agreement, Transocean was also sentenced to five years of probation, the maximum term of probation under law, the Justice Department said.
A separate proposal for a civil consent decree is pending before U.S. District Judge Carl J. Barbier of the Eastern District of Louisiana, and that proposal would impose a record $1 billion civil Clean Water Act penalty, the Justice Department said.