OREANDA-NEWS. The US Supreme Court today refused to hear an appeal brought by BP and US independent Anadarko that could have slashed their potential Clean Water Act penalties arising from the 2010 Deepwater Horizon spill.

The high court let stand a June 2014 decision by the Fifth Circuit Court of Appeals that rejected the companies' argument that oil that passed through the blowout prevent and riser sitting atop the out-of-control Macondo well could not be deemed as having been discharged "from" the well.

A decision by the Supreme Court to take the case could have been significant for well operator BP and minority partner Anadarko. US district court judge Carl Barbier is due to issue a ruling that will access Clean Water Act fines in the wake of the worst oil spill in US offshore history.

BP faces a maximum liability of $13.7bn in Clean Water Act penalties stemming from the spill, based on Barbier's ruling in January that 3.19mn bl were spilled. Barbier has found that BP was "grossly negligent" in its handling of the Macando well.

The Clean Water Act stipulates a fine of $1,100/bl for violations, which rises to $4,300/bl in the event of gross negligence. The US government did not pursue a gross negligence claim against Anadarko.

In asking the court to hear the case, BP had argued that "staggering" sums of money were at stake. But Barbier is expected to find for a less-than-maximum penalty against BP, in recognition of the company's cleanup efforts and payments to claimants affected by the spill.

BP said it has paid $14.2bn in response and cleanup and $16.7bn in legal claims, as well as $4bn after pleading guilty to 14 criminal counts stemming from the spill.

BP declined to comment on the court's decision. Andarko could not be reached for comment.

BP had a 65pc stake in the Macondo well, while Andarko held a 25pc share and Japan's Mitsui held a 10cp stake. Mistui subsidiary Moex agreed to pay $90mn to settle claims by the US government.