Oil giant BP has accused oilfields services firm Halliburton of destroying damaging evidence relating to last year's oil well blast in the Gulf of Mexico in which 11 people were killed.
At a hearing in a New Orleans' court, BP said Halliburton had "intentionally" destroyed test results on its cement product used at the Macondo well.
Halliburton denied this, saying the claims were "without merit".
Cement was a key factor in causing America's worst offshore oil spill.
The blast that followed at the Deepwater Horizon oil rig in April led to the release of 780m litres (206m gallons) of crude oil in the Gulf of Mexico.
BP and Halliburton are locked in a legal battle ahead of a trial on damages early next year.
Through their lawyers, the former partners in the venture are seeking maximum pre-trial advantage, the BBC's Steve Kingstone in Washington reports.
BP made its accusations in a court filing on Monday.
It said that after reviewing the test results, Halliburton "destroyed records of the testing as well as the physical cement samples used in the testing".
The company also said that Halliburton had failed to produce computer modelling evidence, which showed how the cement performed.
In its motion, BP asked for sanctions against Halliburton, claiming that the company's cement slurry was "unstable".
In its turn, Halliburton rejected the claim, saying it would contest it in court.
The world's second-largest oilfields services provider also accused BP of fraud and defamation in the investigation.
The contractor alleged that BP had ordered last-minute changes to the cement.
The two companies traded allegations ahead of the trial over the spill disaster in February.
The trial is expected to apportion blame and quantify damages arising from the spill.
There will also be other phases of the case over clean-up costs and other claims.