NEW ORLEANS (dpa) – When the Deepwater Horizon oil rig was destroyed in an explosion and fire on April 20, 2010 in the Gulf of Mexico, Swiss-based Transocean not only lost nine employees and a multimillion dollar rig, its relationship with BP changed in an instant.

Just prior to the tragic accident, which also killed two other men and caused a massive oil spill, the two companies had celebrated their shared safety record. BP and Transocean had an excellent record in what BP lawyer Mike Brock said was ''the only metric that counts in this case'' – well control – until April 2010.

The two companies are now engaged in a bruising blame game in a courtroom in New Orleans where the US Justice Department, several states and individual plaintiffs are suing BP, Transocean and several other contractors in an effort to determine liability in the accident.

Brock said Monday in his opening statement in the trial that the two companies currently are collaborating on six other wells. He noted that they had touted their joint achievement of drilling the deepest well in history, calling Transocean ''one of the top drillers in the world'' and adding that BP stands by the selection of Transocean as a contractor  for the Deepwater Horizon.

But that was the end of the love. Brock then spent hours accusing its contractor of ''significant failure in well control'' after missing anomalies in the results of a pressure test and signs of a ''kick'' - a massive flow of water, oil, gas and other fluids into the drill pipe – less than an hour before the explosion.

''It's clear that mistakes were made in interpretation of the data (of the test) and the failure to shut in the well, and there is agreement on that in the drilling community,'' said Brock, asserting that if the Transocean employees had read the data properly, the blowout wouldn't have happened.

Brock continued in the same vein on Tuesday in a cross examination of the first witness in the trial, Robert Bea, a professor emeritus at the University of California and an expert in the management of catastrophic risk.

Brock introduced documents showing that Transocean launched a major evaluation of safety processes and culture at the company in October 2009 conducted by Lloyds. It revealed problems with the 21-days-on, 21-days-off work schedule of its employees who were quoted in the report as saying they ''seem like they are in another world in the last week.''

He said a Transocean employee in a decision-making capacity on the rig the night of the explosion was on the final day of his 21 days on the job.

The finger-pointing is expected to continue throughout the trial, which is in its first phase.

Transocean, the world's largest offshore-rig contractor, is not speaking publicly about the trial, but provided a statement saying ''the facts in the case are on Transocean's side and our legal team will prove that in New Orleans.''

It points out that it is an oil exploration company, while BP designed the rig, did all geological surveys and stood to profit once the well started to produce oil. And it says BP had great things to say about Transocean until the Deepwater Horizon disaster.

Transocean, which has 18,700 employees worldwide, provides rigs for all types of petroleum companies in offshore drilling markets that include exploration in the United States, Canada, Brazil, Britain and Norway.

A safety expert said on Tuesday at the trial of energy giant BP that the company had been warned far in advance of the Deepwater Horizon spill that its safety procedures at the oil rig were inadequate.

The expert said BP did not apply what it called its ''cornerstone for safety'' at the Deepwater Horizon rig in the Gulf of Mexico before it exploded in April 2010 and resulted in the death of 11 workers and a massive oil spill.