"Halliburton has stated publicly that it tested the Macondo cement before pumping it on April 19th and 20th, and that its tests indicated the cement would be stable, " Bartlit's letter said.

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Many drillers already run cement logs and do pressure tests and store flowback water safely.

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As part of the investigation, the letter said, Chevron conducted independent tests of similar cement slurry materials supplied by Halliburton and found the mix to be unstable.

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The commission's 13 key points focused on tests done to check the cement used in the well, decisions made by BP when plugging the well and the actions of those at the company in the hours before the disaster aboard the Deepwater Horizon rig.

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The letter from Fred Bartlit Jr. to the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling said that tests in February on a cement slurry similar to what was used on the Macondo well showed instability -- and that both companies had the data.

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The report, which also blamed insufficient regulation as a reason for the disaster, has recommended a standardization of procedures related to the events that led to the spill such as testing cement barriers and interpreting the results of those tests.

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That information revealed the two February tests by Halliburton of a slightly different cement slurry mix that showed it was unstable, the letter said.

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Bartlit emphasized in his letter Thursday that cementing failures are a known hazard in the oil industry, with specific tests such as a "negative pressure test" and "cement evaluation logs" designed to identify cementing problems.

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