The Macondo well sent 4.9 million barrels of oil -- 205.8 million gallons -- into the gulf before it was capped, scientists in the Flow Rate Technical Group said. The number far exceeds previous estimates and all but established the Deepwater Horizon disaster as the worst oil spill ever in the gulf, The Washington Post reported.
It also ranks second on Wikipedia's list of largest known spills behind the Lakeview Gusher in California that spilled 378 million gallons between May 1910 and September 1911. The 1991 Gulf War spill in the Middle East leaked an estimated 84 million to 250 million gallons.
The research group, working with the U.S. Geological Survey and the U.S. Department of Energy, said the BP well initially gushed 62,000 barrels of oil daily. The number fell to 53,000 barrels a day until the flow stopped July 15, when the damaged well was capped and sealed, the scientists said.
An attempt to begin plugging the well by pumping in mud and cement sustained a temporary setback Monday, the British company said on its Web site.
"During final preparations to commence with the injectivity test, a small hydraulic leak was discovered in the capping stack hydraulic control system," BP said in a statement. "The injectivity test, previously announced to take place today, will be rescheduled until the leak is repaired.
"It is anticipated that the injectivity test and possibly the static kill will take place Tuesday."
The operation was previously delayed for several days while crews cleared debris from Tropical Storm Bonnie.
BP Chief Operating Officer Doug Suttles said he had "a lot of confidence we'll be successful," CNN reported Monday.
The static kill will be followed by a final "bottom kill" once a relief well intercepts the ruptured well. BP said that process could start five to seven days after the static kill is finished.
The government's lead official on the oil cleanup warned, however, against looking too far ahead.
"We should not be writing any obituary for this event," national incident commander Thad Allen, a retired U.S. Coast Guard admiral, said Sunday.
Homeland Security Secretary Janet Napolitano traveled to New Orleans Monday to review the oil spill response with federal, state and local officials.
Her trip comes a day after Allen dismissed accusations by a congressional member that federal officials let BP use excessive amounts of chemical dispersants to break up the oil.
Rep. Edward J. Markey, D-Mass., chairman of the House Energy and Environment Subcommittee, said in a letter to Allen that despite a federal directive restricting their use, BP "carpet-bombed the ocean with these chemicals, and the Coast Guard allowed them to do it."
Allen said the use of dispersants was "very disciplined" and employed when oil was spotted by surveillance aircraft and no other cleanup method of cleaning was available.
BP also rejected Markey's allegations, saying it worked with the Environmental Protection Agency and the Coast Guard from the start. Suttles said the company is funding research on the long-term effects of the spill, including the use of dispersants.