BP and Haliburton knew of cement flaws on the Macondo well weeks before the blowout that caused the oil spill in the Gulf of Mexico, a White House panel said.

Fred Bartlit, lead investigator for the US presidential commission on the oil spill, said the cement mixture used to seal the well failed in three out of four laboratory tests before the explosion on 20 April 2010.

Haliburton and BP were aware of flaws in the cement slurry, similar to the one used to seal the Macondo well, as early as 8 March 2010, but chose not to act upon that data, Bartlit added.

In a letter to the National Commission Bartlit said the companies should have considered redesigning the foam slurry before pumping it at the Macondo well.

BP and Transocean were also accused of misinterpreting or choosing not to conduct tests to identify faulty cement work on the well.

However, Halliburton said the foam cement design used at the Macondo well was not the cause of the incident.

The 20 April rig explosion killed 11 workers, caused a massive oil leak and forced the US Government to establish a moratorium for six months on deepwater drilling.