BP PLC's internal investigation into the Deepwater Horizon disaster puts considerable blame on Halliburton Co., which developed and pumped the special cement supposed to seal the bottom of the well that ended up spewing millions of barrels of oil into the Gulf of Mexico.

BP concluded that the cement failed to do one of its main jobs: preventing natural gas from flowing into the well. This was the first in a chain of failures that led to the deadly explosion in April, the report says.

Once...