An inadequate cementing job to temporarily cap the Macondo oil and gas well and a series of failures to recognize the impact of such inadequacies led to the largest oil spill in U.S. history, according to a final report released last week by the Department of the Interior’s Bureau of Ocean Energy Management, Regulation & Enforcement. The April 20, 2010, accident killed 11 workers and leaked nearly 5 million barrels of oil into the Gulf of Mexico. Although the exact cause of the cementing failure remains unknown, the long-awaited report says BP, as the well operator, was ultimately responsible for safety. However, it also says Transocean, the owner of the Deepwater Horizon drilling rig, and Halliburton, a BP contractor responsible for the cementing job, share responsibility. The report cites many failures largely driven by BP’s desire to limit costs by quickly completing the well-capping operation and removing the drilling rig. It notes the rig operators misinterpreted the condition of the cement cap and failed to notice the release of hydrocarbons into the well bore, despite knowing that a similar release on the same rig occurred a month earlier and went undetected for 30 minutes. The report’s release marks the completion of the 16-month investigation.