The crew of an oil rig that exploded in the Gulf of Mexico last year causing one of the worst oil spills in US history ignored warning signs a disaster was imminent, an investigator said Friday.

Marshall Islands deputy maritime affairs commissioner Bill Gallagher, who carried out an inquiry into the explosion because the rig was registered in the Pacific nation, said lessons had to be learned from the disaster.

He said there were indications of a problem at the Deepwater Horizon rig before the blast that killed 11 people on April 20 last year but the crew failed to act.

"There were multiple signs that there were issues at the well itself, indicators, pressure testing, things of that nature were going on," Gallagher told Australia's ABC radio Friday.

"There were signs that there were some problems with the well...the blow out started and then, of course, the disaster followed shortly thereafter."

Gallagher, whose report into the incident was released on Wednesday, also cited "deviation" from drilling rig control engineering standards as a reason for the disaster.

"These factors contributed to the substantial release of liquid and gaseous hydrocarbons, which culminated in explosions, fire, the loss of 11 lives, the eventual sinking and total loss of the Deepwater Horizon, and the release of hydrocarbons into the Gulf of Mexico," the report said.

Almost five million barrels (210 million gallons) of oil spilled into the Gulf of Mexico after the rig's failure, causing enormous environmental damage.

British oil giant BP last month estimated the total clean-up cost at $40.7 billion.

Gallagher said his report did not attempt to determine who was responsible for the spill, an issue which is the subject of legal action in the US between BP and the rig's operator Transocean Offshore Deepwater Drilling.

"It's not for us to assign blame," he said.

A US Coast Guard report in April found Transocean had "serious safety management system failures and a poor safety culture", while a US presidential commission in January slammed "systemic" failures in oil industry safety practices.

The commission called for an overhaul of industry safety measures and the establishment of a tough new safety watchdog to avoid a repeat of the disaster.

Under maritime law, oil rigs such as the Deepwater Horizon are classified as ships, meaning they can be registered in jurisdictions such as the Marshall Islands and Panama.

The Gallagher report said inspectors acting on hehalf of the Marshall Islands inspected the Deepwater Horizon in December 2009, four months before the accident, and found it met safety, security and environmental standards.

earlier related report
Exxon Mobil battles over gulf oil field
Washington (UPI) Aug 19, 2011 - Exxon Mobil Corp. has filed a lawsuit against the U.S. government to reverse an Interior Department decision to cancel offshore oil and gas leases in the Gulf of Mexico.

Exxon Mobil, which has headquarters in Texas, is suing to retain three leases on drilling rights in what it calls the Julia Field, The Wall Street Journal reports. The Interior Department says the leases have expired and Exxon hasn't met requirements for lease extension. Two other leases are yet to expire.

The oil company said the area in question holds an estimated 1 billion barrels of recoverable oil.

Julia, considered one of the gulf's largest oil finds, is about 250 miles southwest of New Orleans.

Exxon Mobil has a 50 percent interest in the leases along with Norway's Statoil, which has also joined in suing the Interior Department.

Exxon Mobil's lawsuit says the government has granted "thousands" of extensions over time and that the government's denial of the extension relied on legal interpretations that it "had never before applied and had never before articulated."

Exxon Mobil spokesman Patrick McGinn maintains that such extensions were traditionally granted as a matter of course.

"You state your case and you got it," he told the Journal, noting that the government's refusal "was unexpected."

The extensions are "fairly common," says Elmer P. Danenberger III, a former federal official who oversaw U.S. offshore-drilling rules until his 2009 retirement.

"I can honestly say that people who manage that program are really strict, which they need to be or it will be abused," he said to the Journal. "If you don't have a commercial discovery and a plan for moving ahead at the end of the lease term … that's it."

In its suit, Exxon Mobil says the government stands to reap millions of dollars in bonuses and royalties by signing replacement leases.

The suit comes after more rigorous regulatory scrutiny of drilling activities following the April 2010 blowout of BP's Deepwater Horizon well in the Gulf.

"Our priority remains the safe development of the nation's offshore energy resources, which is why we continue to approve extensions that meet regulatory standards," a spokeswoman for the Interior Department said. "We are reviewing the complaint in accordance with standard procedures."

Tens of billions of dollars of oil could slip through Exxon Mobil's hands because the company failed to follow federal rules for getting a lease extension while it moved forward with plans to get the oil out of the ground, the Journal says.