By Daniel Gilbert 

When a federal judge ruled last fall on who was to blame for the 2010 Deepwater Horizon disaster, he didn't point a finger at Anadarko Petroleum Corp.

But the energy company is facing a pollution penalty of as much as $3.5 billion because it owned 25% of the oil well drilled by the ill-fated rig, and would have gained a quarter of the crude it pumped if the well hadn't exploded.

Now Anadarko, one of the largest U.S. energy producers, is set to battle federal prosecutors in a trial beginning Jan. 20. It will argue alongside BP PLC, which operated the well known as Macondo. A judge will determine how much each company should pay per barrel spilled.

Anadarko paid BP $4 billion in 2011 to release it of any liability from third-party claims and certain environmental fines. But federal and appellate judges have held that Anadarko is still liable under the Clean Water Act.

"Any penalty that is not measured in billions of dollars would go largely unnoticed at a company the size of" Anadarko, Justice Department lawyers wrote in December. Citing Anadarko's limited role as an investor in the well, the government concludes the firm should pay more than $1 billion but "well below" the maximum.

A spokesman for Anadarko declined to comment and pointed to its regulatory and court filings. In those documents, the company, which has a stock-market value of about $39.73 billion, says it should pay no penalty.

"Anadarko was a faultless, non-operating investor" in the Deepwater Horizon venture, its lawyers contend, and penalizing it "could be counterproductive to offshore safety."

At trial, at least one Anadarko witness is expected to testify that fining the company would create an incentive for investors in a well to take a more active role. The company says that this could "confuse lines of authority, delay critical decisions and be counterproductive to safety," according to court pleadings.

Anadarko has set aside $90 million to pay for any penalty. It tried to settle the case for that amount last July, but was rebuffed by the U.S. government.

Mitsui & Co.'s MOEX Offshore, another Deepwater Horizon investor, reached a $90 million settlement with the Justice Department in 2012, including $70 million to resolve violations under the Clean Water Act.

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