WASHINGTON (AFP) – The US government on Monday said BP's ruptured well in the Gulf of Mexico gushed an estimated 4.9 million barrels of oil, making it the largest accidental oil spill of all time.
"Overall, the scientific teams estimate that approximately 4.9 million barrels of oil have been released from the well," the joint response command that includes BP and the US government said in a statement describing the new estimate.
"Not all of this oil and gas flowed into the ocean; containment activities conducted by BP under US direction captured approximately 800,000 barrels of oil prior to the capping of the well," they said.
The 4.9 million barrels is at the upper end of an earlier official estimate, which said that between 3.0 million and 5.3 million barrels had spewed from the well between April 20, when the BP-leased Deepwater Horizon rig exploded, and July 15, when a cap placed over the wellhead was finally sealed.
The refined estimates "are the most accurate to date and have an uncertainty of plus or minus 10 percent," according to the statement.
The 4.1 million uncontained barrels estimated to have spewed into the water make the spill the biggest accidental oil disaster in the history of the petroleum industry, and second only to the intentional release of crude by Iraqi forces during the 1991 Gulf War.
The previous largest accidental spill was a 1979 disaster -- also in the Gulf of Mexico -- in which 3.3 million barrels gushed from the Ixtoc-1 well after an explosion on a rig operated by Mexican state oil company Pemex.
The BP spill revision was based on "new pressure readings, data and analysis" of oil reservoir modeling studied by teams comprised of federal and independent US scientists, including a Department of Energy team of scientists led by President Barack Obama's energy secretary, Steven Chu, the statement said.
"The revised estimates are part of this administration's ongoing commitment to ensuring that we have the most accurate information possible," Chu said.
When the well first ruptured, "62,000 barrels of oil per day were leaking from the well," beyond the 35,000 to 60,000 barrels most recently estimated by US authorities, but the flow rate decreased to 53,000 barrels per day just before the well was capped, the statement said.
"As a result of depletion of the hydrocarbon reservoir, the daily flow rate decreased over the 87 days prior to the well's closure," according to the statement.
The new figures are based in part on analysis of high-resolution videos taken by remotely operated underwater vehicles, acoustic technologies, measurements of oil collected by vessels on the surface, and readings of pressure measurements inside the containment cap.
"Government scientists will continue to analyze data and may in time be able to further refine this estimate," the statement said.
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