



A federal judge determined on Thursday that more oil than BP estimated spilled into the Gulf of Mexico following a rig explosion in 2010, a decision that could potentially cost the London-based oil giant more than $13bn.



US district judge Carl Barbier ruled that 3.19m barrels – just under 134m gallons – were discharged into the Gulf after a rig explosion at BP’s Macondo well. The number is more than the 2.4m barrel figure BP had argued for and less than the government’s estimate of about 4.2m, a figure that could have meant $18bn in maximum penalties under the Clean Water Act.

Those penalties are to be determined in a trial set to open on Tuesday. In pre-trial briefs, the government has argued that the oil giant should pay as much as $4,300 per barrel spilled. The discharge figure Barbier settled on Thursday means maximum penalties could reach about $13.7bn – but he has not yet decided how much per barrel BP must pay. BP has argued that the penalties should be lower than what the government is asking for, but has not offered a specific figure.

Barbier’s finding – a figure roughly midway between the government’s and BP’s estimates – came more than a year after a trial during which the judge found that BP acted with “gross negligence” in the 2010 explosion of the Deepwater Horizon offshore rig. BP is appealing.

“Both sides presented evidence to support their cumulative flow estimates, and each mounted effective attacks on the other’s calculations,” Barbier wrote. “There is no way to know with precision how much oil discharged into the Gulf of Mexico. There was no meter counting off each barrel of oil as it exited the well. The experts used a variety of methods to estimate the cumulative discharge. None of these were perfect.”

Lawyers for BP argue that the company already faces costs totaling $42bn, including a $14bn response and cleanup effort. They say a low-end penalty would accomplish the Clean Water Act purposes of deterring environmentally dangerous behavior and encouraging effective cleanup responses.

A BP spokesman, Geoff Morrell, reiterated that stance in a statement on Thursday evening.

In a 47-page ruling recapping BPs efforts to control the spill and the conflicting evidence of how much was lost, Barbier said about 168m gallons of oil was released from the well’s reservoir but the figure was reduced to about 134m gallons after recovery efforts.