HOUSTON/WASHINGTON Failure to react to repeated signs of problems with BP Plc's Macondo oil well in the Gulf of Mexico and bypassing basic well control standards caused last year's deadly blowout, the flag state for the drilling rig that exploded and sank said on Wednesday.
The Marshall Islands, where Transocean Ltd registered the doomed Deepwater Horizon rig, also said in a report on its investigation that failure to follow well abandonment plans approved by U.S. regulators played a part.
The rupture and explosion killed 11 workers and spewed more than 4 million barrels of crude into the Gulf in the worst-ever U.S. offshore oil spill.
The report did not specifically blame any of the companies involved, from well owner BP and driller Transocean to blowout preventer maker Cameron International Corp and well-sealing cement maker Halliburton.
By sharp contrast, the Coast Guard and U.S. Bureau of Ocean Energy Management in April released a draft report citing serious safety lapses by Transocean in the lead-up to the accident.
Transocean has strongly disputed those conclusions.
Bill Gallagher, the Marshall Islands' senior deputy commissioner of maritime affairs, told Reuters in an interview that his agency's report was meant to "put forth some observations to the International Maritime Organization" to suggest possible changes to enhance rig safety.
"We're not going into gross negligence" or other legal issues, he said.
The report recommended better communication between flag states and coastal states -- those that register rigs and regulators that oversee offshore operations -- to ensure both know of conditions that could affect rig and worker safety.
(Reporting by Kristen Hays in Houston and Ayesha Rascoe in Washington; Editing by Dale Hudson)