Halliburton officials knew weeks before the fatal explosion of the BP well in the Gulf of Mexico that the cement mixture they planned to use to seal the bottom of the well was unstable but still went ahead..., the presidential commission investigating the accident said on Thursday. In the first official finding of responsibility for the blowout..., the commission staff determined that Halliburton had conducted three laboratory tests that indicated that the cement mixture did not meet industry standards. The result of at least one of those tests was given on March 8 to BP, which failed to act upon it, the panel’s lead investigator...said...Although [he] did not specifically identify the cement failure as the sole or even primary cause of the blowout, he made clear...that if the cement had done its job..., there would have been no accident...Halliburton has said repeatedly in public testimony that it tested and used a proper cement formula and that BP’s flawed well design and poor operations caused the disaster...A BP spokesman said the company would have no comment. [also refers to Transocean]