The US government report issued in September 2011 stated that BP is ultimately responsible for the spill, and that Halliburton and Transocean share some of the blame.[20][322] The report states that the main cause was the defective cement job, and Halliburton, BP and Transocean were, in different ways, responsible for the accident.[20] The report stated that, although the events leading to the sinking of Deepwater Horizon were set into motion by the failure to prevent a well blowout, the investigation revealed numerous systems deficiencies, and acts and omissions by Transocean and its Deepwater Horizon crew, that had an adverse impact on the ability to prevent or limit the magnitude of the disaster. The report also states that a central cause of the blowout was failure of a cement barrier allowing hydrocarbons to flow up the wellbore, through the riser and onto the rig, resulting in the blowout. The loss of life and the subsequent pollution of the Gulf of Mexico were the result of poor risk management, last‐minute changes to plans, failure to observe and respond to critical indicators, inadequate well control response, and insufficient emergency bridge response training by companies and individuals responsible for drilling at the Macondo well and for the operation of the drilling platform.[20]