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The companies involved in the worst offshore oil spill in U.S. history are trying to prevent government investigations blaming them for the disaster from being used against them by the people and businesses who are suing them.

Billions of dollars are potentially at stake in a trial scheduled for February to determine whether rig owner Transocean can limit what it pays those making claims under maritime law and to assign percentages of fault to Transocean and other companies involved.

BP, Transocean and cement contractor Halliburton filed motions late Monday in federal court in New Orleans seeking to keep certain government oil spill reports out of the civil case. BP also wants a judge to bar plaintiffs' lawyers from using past criminal, civil and regulatory proceedings against the British firm in the civil case.

The filings deal with the two most comprehensive federal investigations of the disaster. One that was issued in September by the U.S. Coast Guard and the agency that regulates offshore drilling concluded that BP bears ultimate responsibility for the disaster. The other report by the presidential oil spill commission blamed the blowout on a series of failures involving all the players.

There was no immediate ruling.

The Deepwater Horizon explosion in the Gulf of Mexico off Louisiana in April 2010 killed 11 rig workers and led to more than 200 million gallons of oil spewing from a well a mile (two kilometers) beneath the sea. The well was capped three months later, but not before hundreds of miles of coastline were stained, seafood and tourism businesses were devastated, and a fragile ecosystem was damaged.

BP PLC, which owned the well and was leasing the rig from Transocean Ltd., has already spent or committed tens of billions of dollars on cleaning up the oil and compensating victims. It is at risk of having to pay out billions more depending on the outcome of the civil trial involving hundreds of lawsuits. Government fines and penalties also could add significant liability.

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