A US judge said energy giant BP faces a maximum fine of $13.7 billion for the 2010 Gulf of Mexico oil spill, a sum reduced by several billion dollars.
A fine of up to $18 billion had originally been set as a possible penalty, based on government estimates that 4.19 million barrels of oil were released into the Gulf of Mexico.
But US federal court judge Carl Barbier said Thursday in New Orleans the penalty should be based on only 3.19 million barrels.
A final penalty will be determined beginning Tuesday at a trial to settle an exact sum.
In September, Barbier concluded that the Deepwater Horizon drilling rig blowout, which killed 11 and spilled millions of barrels of oil into Gulf waters, occurred after inadequate care in drilling.
In pleading guilty to the spill, BP agreed to pay the government $4.5 billion to settle criminal charges. It also agreed in 2012 to settle damage claims by businesses and individuals for about $7.8 billion.
Meanwhile the company has doled out some $10 billion to companies, individuals and local authorities who agreed not to file suit and has spent around $14 billion on cleaning the badly damaged coast.
The National Wildlife Federation said in April that scientific studies on 14 different types of creatures affected by the spill show that long-lasting harm was done to dolphins, sea turtles, tuna, loons and other animals in the region.