Story highlights Halliburton destroyed computer tests after Deepwater Horizon, prosecutors say

Tests showed "little difference" between what it urged and what BP did, they say

BP and Halliburton are still battling over the disaster in court

BP had accused Halliburton of destroying evidence in 2011

Oilfield services giant Halliburton will plead guilty to destroying computer test results that had been sought as evidence in the Deepwater Horizon disaster, the Justice Department announced Thursday.

Company officials threw out test results that showed "little difference" between the number of devices Halliburton said was needed to center the cement casing in the well at the heart of the disaster and the number well owner BP installed, according to court papers. The issue has been key point of contention between the two companies in hearings and litigation ever since the April 2010 blowout.

BP and Halliburton are still battling over responsibility for the disaster in a New Orleans federal courtroom. BP had no comment on the plea agreement Thursday evening.

The Deepwater Horizon blowout killed 11 rig workers and unleashed the biggest oil spill in U.S. history. The federal government estimates more than 200 million gallons poured out of the ruptured well, located nearly a mile underwater off southeastern Louisiana. The environmental effects of the disaster are still being determined , and BP says it has paid out $32 billion for cleanup, compensation and penalties.

The Halliburton tests, which used a computer simulation, were run in May and June 2010. After each of the two rounds of tests, a Halliburton executive ordered the simulations destroyed, the charges state.

"During ensuing civil litigation and federal criminal investigation by the Deepwater Horizon Task Force, subsequent efforts to forensically recover the deleted Displace 3D computer simulations from May/June 2010 were unsuccessful," according to prosecutors.

In a court filing in 2011, BP accused Halliburton of destroying evidence -- including "inexplicably missing" computer modeling results -- "to eliminate any risk that this evidence would be used against it at trial."

Halliburton has agreed to pay the maximum fines available, be put on probation for three years and cooperate with federal agencies that are still investigating the spill, the Justice Department said in a statement announcing Thursday's agreement. In addition Halliburton has made a $55 million "voluntary contribution" to the National Fish and Wildlife Foundation, a payment "that was not conditioned on the court's acceptance of its plea agreement."

A federal report in 2011 concluded that BP, Halliburton and Deepwater Horizon owner Transocean all violated federal offshore safety regulations and shared responsibility for the disaster.