New Orleans, Louisiana (CNN) -- A crucial test -- meant to determine whether an effort to seal the ruptured BP oil well in the Gulf of Mexico could proceed -- has been delayed because of a small leak, the company said Monday.
The "injectivity" test is now likely to happen Tuesday, BP said. That's the same day the company could also conduct the "static kill," one of two efforts planned to cap the leaking well once and for all.
"During final preparations to commence with the injectivity test, a small hydraulic leak was discovered in the capping stack hydraulic control system. The injectivity test, previously announced to take place today (Monday), will be rescheduled until the leak is repaired," BP said in a statement.
In the test, "base oil" will be pumped into the ruptured well bore to determine if it will go back into the reservoir, said Kent Wells, BP's senior vice president. The test will start with pumping one barrel per minute, then two, then three. How much is pumped will depend on how the test goes, Wells said. He added the test is meant to help officials decide whether adjustments need to be made on "how and if" the static kill will proceed.
The static kill would involve pouring mud, possibly followed by cement, into the well from above. The goal is to push all the oil back into the reservoir, and seal the well.
Meanwhile, scientists charged with determining the flow from the leaking well said Monday that roughly 4.9 million barrels of oil have seeped from the well. Previously, the same group had put the total estimate of oil leaked from the well prior to it being capped on July 15 at between 3 million and 5.2 million barrels.
The moment the well was capped, scientists said some 53,000 barrels of oil per day were leaking from the well, while roughly 62,000 barrels of oil were likely seeping per day from the oil well at the start of the spill.
The static kill, which officials have said could take up to 61 hours, could be followed by a final "bottom kill," after a relief well intercepts the crippled well -- a step estimated to start some five to seven days after the static kill is complete. If the injectivity test is not successful, the static kill procedure would be skipped and the bottom kill effort would proceed, BP's Wells said Monday.
Federal officials remain cautious.
"I don't think we can see this as the end-all, be-all, until we actually get the relief wells done," said Thad Allen, the government point man on the Gulf spill.
Speaking to reporters, Allen also rejected accusations by a congressional subcommittee that federal officials allowed BP to use excessive amounts of chemical dispersants.
BP used the chemicals to break up oil after the April 20 Deepwater Horizon rig explosion that killed 11 workers and set in motion the worst oil spill in U.S. history.
Despite a federal directive restricting their use, BP "carpet bombed the ocean with these chemicals, and the Coast Guard allowed them to do it," said Rep. Edward J. Markey, chairman of the House Energy and Environment Subcommittee.
Markey said the Coast Guard ignored a directive to allow dispersants only on rare occasions.
Allen, who has defended the use of dispersants as a "very disciplined" procedure, has said field commanders used dispersants when oil was spotted by surveillance aircraft and no other method of cleaning it up was available in the area.
"The goals laid out with the EPA were largely met. ... Now on a daily basis you could find exceptions, and there were times when maybe not everybody agreed on what we should do. But the fact of the matter is folks are managing these conditions on-scene, tactically, and have to make decisions without complete information, sometimes under conditions of uncertainty," said Allen, a recently retired Coast Guard admiral.
BP also dismissed Markey's allegations and said it has worked closely with the Environmental Protection Agency and the Coast Guard from the start.
The EPA said that testing found eight dispersants, including one used in combating the Gulf of Mexico oil disaster, are no more toxic when mixed with oil than the oil alone. The tests prove that the oil itself, not the dispersants, is "enemy No. 1," Paul Anastas, EPA assistant administrator for research and development, told reporters on a conference call.
CNN's Vivian Kuo contributed to this report.