Regulator pins responsibility for Gulf spill on BP but blame shared

The long-awaited federal government report into the Deepwater Horizon disaster has blamed cost-cutting by BP for the explosion that sank the rig, killed 11 workers and left oil billowing into the Gulf of Mexico for almost three months.

The 16-month investigation pinned blame, too, on BP's partners and contractors on the rig, but said that BP, as designated operator, bore ultimate responsibility and had repeatedly let cost considerations creep into its decisions about how to operate the well.

"BP's cost or time saving decisions without considering contingencies and mitigation were contributing causes of the Macondo blowout," wrote the authors from the Bureau of Ocean Energy Management Regulation and Enforcement, the drilling regulator. Deepwater Horizon was the name of the rig, Macondo is the name of the well that it drilled.

"BP, as the designated operator under BOEMRE regulations, was ultimately responsible for conducting operations at Macondo in a way that ensured the safety and protection of personnel, equipment, natural resources, and the environment," the report concluded.

The BOEMRE report, written with the US Coast Guard after months of investigation, interviews and public hearings, is the most exhaustive to date on the disaster, which began with an explosion on 20 April last year. The resulting oil spill was one of the largest in US history, and BP estimates the cost of capping the well, cleaning up the ocean and coastal areas and compensating businesses in the fishing and tourism industries could hit $40bn (£25bn).

As well as setting out in detail the catalogue of errors that led to the explosion, the report also examined the culture at BP.

"From the outset, BP acknowledged its role in the accident and has taken concrete steps to further enhance safety and risk management throughout its global operations," BP said. "We continue to encourage other parties to acknowledge their roles in the accident and make changes to help prevent similar accidents in the future."

The oil giant is involved in multibillion-dollar legal disputes with its partner in the rig, Transocean, and its contractor, Halliburton, which was responsible for the cement casing in the well that failed. The proportion of responsibility that the courts ultimately apportion to each party will determine their respective liability for paying compensation claims.

In the days leading up to the accident, BP made a series of decisions that complicated cementing operations and may have contributed to the ultimate failure of the cement on the well, yesterday's report found. The British company failed to communicate these decisions and the "increasing operational risks" to Transocean.

"As a result, BP and Transocean personnel onboard the Deepwater Horizon... did not fully identify and evaluate the risks inherent in the operations that were being conducted at Macondo," the investigators said. Transocean workers missed an opportunity to address the cement problems when they misinterpreted a critical test of the well's cement barriers.