(BBC News) -- Cement used to seal the Macondo well may have contributed to the blowout that caused the Gulf of Mexico oil spill, US investigators have found.
Both BP, which owned the well, and Halliburton, the contractor responsible for the cement, were aware of tests showing it was unstable, they said. Halliburton has denied the claims, saying the tests were invalid as they were on a different kind of cement.
The 20 April blowout led to the worst environmental disaster in US history. Hundreds of miles of coast were polluted. The well was finally capped on 15 July, after an estimated 4.9m barrels of oil (171m gallons) had leaked into the sea, and fully sealed last month.