Updated at 11:26 p.m. ET
British Petroleum once downplayed the possibility of a catastrophic accident at an offshore rig that exploded, causing the worst U.S. oil spill in decades along the Gulf Coast and endangering shoreline habitat.
In its 2009 exploration plan and environmental impact analysis for the well, BP suggested it was unlikely, or virtually impossible, for an accident to occur that would lead to a giant crude oil spill and serious damage to beaches, fish and mammals.
"The sort of occurrence that we've seen on the Deepwater Horizon is clearly unprecedented," BP spokesman David Nicholas told The Associated Press on Friday. "It's something that we have not experienced before ... a blowout at this depth."
BP's 52-page exploration plan for the Deepwater Horizon well, filed with the federal Minerals Management Service, says repeatedly that it was "unlikely that an accidental surface or subsurface oil spill would occur from the proposed activities."
And while the company conceded that a spill would impact beaches, wildlife refuges and wilderness areas, it argued that "due to the distance to shore (48 miles) and the response capabilities that would be implemented, no significant adverse impacts are expected."
Robert Wiygul, an Ocean Springs, Miss.-based environmental lawyer and board member for the Gulf Restoration Network, said he doesn't see anything in the document that suggests BP addressed the kind of technology needed to control a spill at that depth of water.
"The point is, if you're going to be drilling in 5,000 feet of water for oil, you should have the ability to control what you're doing," he said.
Although the cause of the explosion was under investigation, many of the more than two dozen lawsuits filed in the wake of the explosion claim it was caused when workers for oil services contractor Halliburton Inc. improperly capped the well a process known as cementing. Halliburton denied it.
According to a 2007 study by the federal Minerals Management Service, which examined the 39 rig blowouts in the Gulf of Mexico between 1992 and 2006, cementing was a contributing factor in 18 of the incidents. In all the cases, gas seepage occurred during or after cementing of the well casing, the MMS said.
While the amount of oil in the gulf already threatened to make it the worst U.S. oil disaster since the Exxon Valdez spill in Alaska in 1989, one expert emphasized that it was impossible to know just how much oil had already escaped and that it could be much more than what BP and the Coast Guard have said.
Even at current estimates, the spill could surpass that of the Valdez which leaked 11 million gallons in just two months.
Ian R. MacDonald, an oceanography professor at Florida State University, said estimates from both Coast Guard charts and satellite images indicate that 8 million to 9 million gallons had spilled by April 28.
"I hope I'm wrong. I hope there's less oil out there than that. But that's what I get when I apply the numbers," he said.
Coast Guard Admiral Mary Landry brushed off such estimates that suggested the rate of the leak was five times larger than official estimates.
"I would caution you not to get fixated on an estimate of how much is out there," Landry said. "The most important thing is from Day One we stood corralling resources from a worst-case scenario working back."
Doug Suttles, BP's chief operating officer for exploration and production, said it's impossible to measure the flow. But he said remote cameras show the rate doesn't appear to have changed since the leak was discovered.
"This is highly imprecise, highly imprecise," Suttles said. "We continue to respond to a much more significant case so that we're prepared for that in the eventuality that the rate is higher."
More on the Gulf Rig Disaster:
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BP, Transocean Accused of Negligence in Spill
Weather Hurts Gulf Oil Fight; Wildlife in Peril
Gulf Oil Spill, by the Numbers
Oil Spill: What Went Wrong?
Oil Spill Creeping Toward U.S. Coast
Pentagon's "Full-Blown Effort" to Halt Spill
Obama on Oil Rig Cleanup
Oil Leak May be 5 Times Worse than Initial Claim
BP Exec: Size of Leak Won't Change our Response
Crews Start Burning Gulf Oil Slick
Fighting Oil with Fire
Man-Made Disaster in the Gulf
New Oil-Rig Safety Rules Eyed Before Blast