BP's former CFO has died. Picture: Reuters.

New Orleans - BP's own investigation of the 2010 Gulf of Mexico spill ignored a phone call between BP supervisors about a critical pressure test that was misinterpreted with deadly consequences, a lawyer for rig owner Transocean Ltd contended in aggressive questioning on Monday.

As a civil trial that will determine blame for the disaster entered its second week, Transocean lawyer Brad Brian pushed BP's global head of safety and operational risk on why the report did not mention that call even though investigators mentioned it in their notes.

The report by BP Plc placed most of the blame for the explosion and spill on Transocean, whose Deepwater Horizon rig, under contract with BP, had been drilling a mile-deep well when a surge of gas caused a blowout that killed 11 workers.

“I think my team's thinking was ... it was mentioned, it wasn't in the form of consulting about it,” replied Mark Bly, the BP executive who headed the company's investigation.

The US Justice Department, Gulf Coast states affected by the spill, and other plaintiffs - all of whom are suing BP, Transocean and other companies - argue that BP put profits over safety in the drilling job, which was over-budget and overdue.

Lawyers for the plaintiffs have argued that had well site leader Don Vidrine heeded concerns of onshore senior drilling engineer Mark Hafle about that pressure test and stopped the operation, the disaster at the Macondo well could have been averted.

London-based BP has acknowledged that engineers misinterpreted the results of the test, but holds both itself and Transocean responsible for that.

Brian also questioned whether Bly and his investigative team looked into whether BP's decisions were driven by saving time and money. “We didn't look at that specific question,” Bly said.

The trial has now entered its second week before US District Judge Carl Barbier in the first of three phases. The first phase focuses on allocation of blame among the companies involved.

Later on Monday, Andrew Hurst, a geology and petroleum geology professor at the University of Aberdeen, Scotland, testified on behalf of the plaintiffs that rock layers where Macondo was drilled are particularly fragile because the area is the site of the second-largest underwater landslide in the world and was the site of an undersea earthquake in 2006.

He said the drilling operation could have left the rock so fragile that cement pumped into it could not bind to the rock as required.

“My opinion is that formation around the bore hole disintegrated,” Hurst testified. “I can't see how anything else could have happened.”

Under cross examination, BP attorney Matt Regan stressed that Hurst's observations about thermal conditions and pressure where BP drilled would apply to the vast majority of such sites, and that many in the industry do not follow his prescribed procedures.

He also asked Hurst whether his conclusions were based on “Macondo specific data” or general observations. Hurst responded that he based his opinions on science, conceding that he did not try to “form a prognosis” for the Macondo well.

The case is In re: Oil Spill by the Oil Rig “Deepwater Horizon” in the Gulf of Mexico, on April 20, 2010, No. 10-md-02179, in the US District Court, Eastern District of Louisiana. - Reuters