Drilling engineers use tons of a thick fluid called drilling mud to lubricate drill bits as they chew through rock.

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Halliburton said that the report "accurately places responsibility on BP as the well owner for its operational decisions, " which included using a heavy fluid designed to keep gas from entering the well, called drilling mud, that was "too light" and probably mixed with the cement at the bottom of the well, and drilling too narrow a well.

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