The explosion at the Macondo well caused the largest offshore oil spill in US history [Gallo/Getty] 

Tests carried out before the catastrophic blowout of a BP oil well in the Gulf of Mexico showed that the cement that was to be used to seal the well was unstable, a US government commission has concluded.

In a letter made public on Thursday, investigators said that US company Halliburton had continued to use the nitrogen foam cement despite three separate tests finding that it was flawed. 

"Halliburton and BP both had results in March showing that a very similar foam slurry design to the one actually pumped at the well would be unstable, but neither acted upon that data," Fred Bartlit, the chief counsel to the commission, said.

"Halliburton [and perhaps BP] should have considered redesigning the foam slurry before pumping it at the Macondo well."

The Macondo well exploded on April 20 killing 11 people and causing the largest offshore oil spill in US history.

Blame game

The cement was supposed to secure the outer casing of the well to prevent hydrocarbons from entering it and potentially causing explosions.

Independent tests conducted for the commission by Chevron on a nearly identical cement mixture to Halliburton's were also released on Thursday. Those results also concluded that the cement mix was unstable.

Halliburton has previously said its tests showed the cement mix was stable, blaming BP's well design and operations for the disaster.

"This gives BP more ammunition to criticise Halliburton and it weakens Hallinburton's position that everything was pumped according to the well design," Bob Cavnar, a Colorado-based energy analyst and blogger, told Al Jazeera.

"The concern here though is that the design of the cement itself might not have been sufficent, but it was also the cement that BP approved. 

"So I think we are going to see the blame game going back and forth for quite some time."

Investor concerns

The criticism of Halliburton's cement job raised investors' concerns it could be forced to bear some of the clean-up costs.

Halliburton's shares tumbled as much as 16 per cent after the panel's findings became public, before recovering to close down nearly eight per cent at $31.68 per share on the New York Stock Exchange.

"The fact that BP and Halliburton knew this cement job could fail only solidifies their liability and responsibility for this disaster," Edward Markey, a Democrat congressman, said.

The commission was careful to underline that the cement seal was not the only factor that led to the accident. Cementing failures are "not uncommon" and the oil industry has developed tests to identify and remedy deficient cement jobs, the report said.

Representatives from the companies involved in the accident, industry executives, technical experts and regulators are due to testify in Washington next month at a hearing into the preliminary findings of the commission.

Source: Al Jazeera and agencies