Published: Jun 24, 2011 2:58 PM EDT
Updated: Jun 24, 2011 2:58 PM EDT

ATLANTA (AP) - BP and Transocean are at odds over who should get possession of a key piece of evidence in the Gulf of Mexico oil spill investigation once additional testing is complete.

Transocean, responsible for maintaining the blowout preventer that failed to stop last year's oil spill, argues it is best equipped to preserve the 300-ton device and it wants it back.

But BP told a federal magistrate judge in a letter filed by the court Friday that the blowout preventer shouldn't be given to one of the defendants in numerous lawsuits filed over the disaster. It said the government should safeguard it at least until the end of a trial set for February related to the lawsuits.

The government has said the blowout preventer failed because of a design flaw and a bent piece of pipe. BP, unsatisfied with the analysis, got court approval for additional testing. The government has said it doesn't expect its conclusions to change, though BP and other companies could use the results of the additional testing to defend themselves in the lawsuits.

The additional testing is wrapping up at a NASA facility in New Orleans, and the court has asked the parties to weigh in on what should be done with the device.

"Transocean has the necessary expertise to transport the BOP to a location of its choosing and is willing to assume the costs associated with the related transportation," Transocean said in a letter to the court.

BP argues the blowout preventer should remain in independent hands to ensure its integrity because it is "one of the most central pieces of physical evidence in this litigation."

A lawyer for the Justice Department told the court that the government wants to retain the control pods and certain other parts of the blowout preventer, but it doesn't object to the rest of the device being returned to Transocean. However, it noted that another government agency, the U.S. Chemical Safety Board, may want to do additional testing if its own.

A ruling was pending.

Eleven workers were killed when the Deepwater Horizon rig exploded off Louisiana on April 20, 2010. Some 206 million gallons of oil spewed from a well a mile beneath the sea before it was capped three months later, according to government estimates. BP owned the well and was leasing the rig from Transocean.

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