Halliburton defended itself Tuesday against accusations it intentionally destroyed evidence about the quality of cement slurry in an oil well that blew out in the Gulf of Mexico.

The cement job on the Macondo well is expected to play a big role in the court battle of who should bear the blame for the blowout that killed 11 workers and led to the nation's worst offshore oil spill.

Investigators with a presidential commission said in February that Halliburton's cement slurry pumped into the bottom of the well was a leading technical cause for the blowout April 20, 2010. Hydrocarbons passed through the cement plug at the bottom of the well and entered the wellbore, the panel said.

Chevron tested Halliburton's cement mix for the commission and found it did not mix properly to be stable, the panel said.

Halliburton engineers have argued that hydrocarbons got into the well other ways. The company said the slurry used in the Macondo well was "designed to be stable."

Spokeswoman Beverly Stafford said testing after the spill was informal and "not conducted on rig samples or in a manner approved by Halliburton."

BP accused Halliburton employees of doing an internal investigation and discarding and destroying early test results after the blowout that found problems. BP said Halliburton's chief cement mixer for Gulf projects testified in depositions that the slurry seemed "thin" to him but that he chose not to write about his findings to his bosses out of fear he would be misinterpreted.

"I didn't want to put anything on an email that could be twisted, and turned," Rickey Morgan, the Halliburton cement expert, said in depositions, according to BP.

The blame game ratcheted up the showdown among BP PLC and its contractors, Halliburton, Transocean Ltd., the drilling company, and Cameron International Corp., the maker of the blowout preventer.

Tyler Priest, a University of Houston historian who specializes in the Gulf oil industry, said the cement failure will be a big issue.

"It seems like the big litigation is going to be between BP and its contractors," Priest said. "There's a lot of money at stake, and it's going to be decided in the courts."

So far, BP, the operator of the Macondo well, has footed the bill for the emergency response and cleanup.

Stafford, the Halliburton spokeswoman, called BP's allegations an attempt to divert attention from its own "poor engineering decisions — decisions that increased the risks of a blowout to save time and money." She accused BP of withholding data needed to design the cement slurry for the Macondo well.

BP is facing the possibility of being found to have acted with gross negligence, a finding that could lead to punitive actions and criminal charges, experts said.

Eric Smith, of Tulane University's Energy Institute, said the stakes are particularly high for BP because a finding of gross negligence could force the company to suspend drilling operations in the Gulf of Mexico, where it is the largest single leaseholder.

"BP doesn't want to be put in a position to not be able to drill in the Gulf of Mexico," Smith said.

The first trial over the Deepwater Horizon disaster is scheduled to start Feb. 27 in New Orleans.