WASHINGTON  The Deepwater Horizon blowout and oil spill in the Gulf of Mexico was an avoidable accident caused by a series of failures and blunders by the companies involved in drilling the well and the government regulators assigned to police them, the presidential panel named to study the accident has concluded.

The companies  BP, Transocean and Halliburton, and several subcontractors working for them  took a series of hazardous and time-saving steps without adequate consideration of the risks involved, the commission reports in a chapter of its final findings, released on Wednesday in advance of the full report, to be published early next week.

The panel also found that company officials had failed to consult with one another on critical decisions and that senior management had paid insufficient attention to the troubled well, which was being drilled a mile under the gulf’s surface.

The commission warned that without major changes, another such accident was likely. “The blowout was not the product of a series of aberrational decisions made by rogue industry or government officials that could not have been anticipated or expected to occur again,” it concluded. “Rather, the root causes are systemic and, absent significant reform in both industry practices and government policies, might well recur.”