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

CNN: STORY HIGHLIGHTS

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.

CNN: STORY HIGHLIGHTS

In the first act, the report claims that Halliburton supplied a cement slurry of its own devising which it should have recognised was not fit for purpose.

ECONOMIST: BP casts the blame for the Gulf oil spill widely

However, the letter said investigators were unsure if that fourth test was completed before the cement slurry was poured at the Macondo well, and that Halliburton reported the positive result to BP after the blowout.

CNN: STORY HIGHLIGHTS

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.

CNN: STORY HIGHLIGHTS

Washington (CNN) -- Oil giant BP and contractor Halliburton knew of potential flaws in the cement slurry used to reinforce the oil well below the Deepwater Horizon rig before it exploded in April, according to a letter Thursday from the lead investigator for a federal probe of the Gulf oil disaster.

CNN: STORY HIGHLIGHTS

Subsequent testing showed that the cement such a slurry produced would have been likely to break down.

ECONOMIST: BP casts the blame for the Gulf oil spill widely

Yet noble intentions do not, of themselves, move concrete, even rotting concrete like the cement-and-pine-cone slurry used to make the Elwha Dam, the first of the two structures to be built.

ECONOMIST: Water in the West (2)

Cement forms an extremely strong, effectively impermeable, seal from a thin slurry that can be pumped pretty easily anywhere, and is the ideal material for this purpose ( Cementing).

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