The owner of the oil rig that exploded in the Gulf of Mexico in 2010 and caused the worst spill in U.S. history will pay more than $1 billion in fines.

Under a settlement with the U.S. Justice Department, Transocean Deepwater acknowledged Thursday that it was criminally negligent when it failed to investigate evidence that the underwater Deepwater Horizon well was not secure. It also pleaded guilty to violating the federal Clean Water Act.

Transocean will pay $1.4 billion in civil and criminal fines and penalties. The money will be used to restore the Gulf region affected by the oil spill, including damaged bird and wildlife habitats.

U.S. Attorney General Eric Holder says Thursday's settlement is a significant step closer to justice for the human, environmental and econometric deviation caused by the oil spill.

The oil rig off the Louisiana coast exploded in April 2010, killing 11 workers. The blast caused millions of liters of oil to gush uncontrollably out of the underwater well for three months.

BP, which leased the well from Transocean, already has pleaded guilty to manslaughter in the 11 deaths and will pay $4.5 billion in criminal charges. A civil settlement is pending.