BP could face fines of $18bn on top of the eye-watering damages and clean up costs already incurred, after a US federal judge ruled that "gross negligence" and "willful misconduct" led to the disastrous oil spill in the Gulf of Mexico in 2010.
The ruling by US District Court Judge Carl Barbier comes as a major blow for the company, which has been trying to prove it was not the only one responsible for the accident, and that its contractors, Halliburton and Transocean, are equally responsible, if not more culpable.
"The Court concludes that the discharge of oil 'was the result of gross negligence or willful misconduct' by BP," Barbier said in his ruling.
"BP's conduct was reckless," he said.
The company could face fines up to $18bn (€13.8bn, £11bn), according to media reports. A fine of $4.5bn was thought to be the maximum amount that could be levied under a "simple negligence" ruling.
BP has so far spent more than $28bn on damage claims and cleanup costs. It has set aside only $3.5bn for fines under the Clean Water Act, as it expected the court would find simple negligence in the case.
Barbier noted that most of the blame for the disaster is to be apportioned to BP and not Transocean and Halliburton.
BP said it would appeal the ruling, which was "not supported by the evidence at trial".
"BP believes that an impartial view of the record does not support the erroneous conclusion reached by the District Court," the company said.
In 2010, the Deepwater Horizon oil rig exploded in the BP-owned Macondo Prospect, which spilled oil into the surrounding Gulf of Mexico waters over a three-month period.
Eleven workers on the rig died in the explosion and environmental devastation slicked its way through the waters, poisoning marine life as well as a number of clean-up workers and Gulf of Mexico residents.
BP has been hit by a number of pieces of civil and criminal litigation from people and businesses affected by the spill. Two phases of the trial over BP's negligence and the amount of oil spill have been completed. The third phase scheduled for January will determine the exact amount of fines to be paid by the company.