The issue of how fast the well is leaking has been murky from the beginning. For several days after the April 20 explosion of the Deepwater Horizon rig, the government and BP claimed that the well on the ocean floor was leaking about 1,000 barrels a day.

A small organization called SkyTruth, which uses satellite images to monitor environmental problems, published an estimate on April 27 suggesting that the flow rate had to be at least 5,000 barrels a day, and probably several times that.

The following day, the government — over public objections from BP — raised its estimate to 5,000 barrels a day. A barrel is 42 gallons, so the estimate works out to 210,000 gallons per day.

BP later acknowledged to Congress that the worst case, if the leak accelerated, would be 60,000 barrels a day, a flow rate that would dump a plume the size of the Exxon Valdez spill into the gulf every four days. BP’s chief executive, Tony Hayward, has estimated that the reservoir tapped by the out-of-control well holds at least 50 million barrels of oil.

The 5,000-barrel-a-day estimate was produced in Seattle by a NOAA unit that responds to oil spills. It was calculated with a protocol known as the Bonn convention that calls for measuring the extent of an oil spill, using its color to judge the thickness of oil atop the water, and then multiplying.

However, Alun Lewis, a British oil-spill consultant who is an authority on the Bonn convention, said the method was specifically not recommended for analyzing large spills like the one in the Gulf of Mexico, since the thickness was too difficult to judge in such a case.

Even when used for smaller spills, he said, correct application of the technique would never produce a single point estimate, like the government’s figure of 5,000 barrels a day, but rather a range that would likely be quite wide.