This is pretty important - not just because they need to know how much oil they have to clean up, but because any fine levied against BP will be based on the number of gallons. (Of course, that assumes they don't file for bankruptcy.)

The Deepwater Horizon well is most likely spewing at least 25,000 barrels of oil a day, and may be producing 40,000 or even 50,000 barrels a day, according to preliminary research from two teams of scientists appointed by the federal government to study the flow from the dark geyser at the bottom of the Gulf of Mexico.

Another scientific team, however, using a different methodology, estimates a somewhat more modest flow of 12,600 to 21,500 barrels.

The numbers are all over the place, acknowledged U.S. Geological Survey director Marcia McNutt in a news conference Thursday announcing the findings. Several other teams are preparing their own figures in what has been a protracted and often frustrating effort to get a handle on exactly how much oil is surging from the Macondo reservoir three and a half miles below the surface of the gulf.

One group, the so-called "plume team," examined video of the leaking riser pipe before it was sheared on June 3. The team concluded that 20,000 to 40,000 barrels may be flowing, with 25,000 to 30,000 barrels being the most likely rate. If that estimate is correct, and the flow has been more or less consistent, approximately 1.3 million to 1.5 million barrels -- or 53.6 million to 64.3 million gallons -- of oil have emerged from the well since the April 20 blowout. That is roughly five to six times the amount spilled in Alaskan waters in 1989 by the Exxon Valdez.

[...] The flow rate is significant on several fronts. First, it gives the government and BP a sense of how much capacity they'll need among surface ships to handle all the oil gushing out the well and up a pipe to the Discovery Enterprise drillship, which is capable of processing only about 18,000 barrels a day. Other ships are being added to the effort. The site above the blown out well has become crowded with 25 to 30 different vessels at any given time, Allen said Thursday.

Rolling Stone says the spill is even bigger, and notes the White House is doing its best to lowball the estimates:

"The upper bound from the plume group, if it had come out, is very high," says Timothy Crone, a marine geophysicist at Columbia University who has consulted with the government's team. "That's why they had resistance internally. We're talking 100,000 barrels a day."

The median figure for Crone's independent calculations is 55,000 barrels a day – the equivalent of an Exxon Valdez every five days. "That's what the plume team's numbers show too," Crone says. A source privy to internal discussions at one of the world's top oil companies confirms that the industry privately agrees with such estimates. "The industry definitely believes the higher-end values," the source says. "That's accurate – if not more than that." The reason, he adds, is that BP appears to have unleashed one of the 10 most productive wells in the Gulf. "BP screwed up a really big, big find," the source says. "And if they can't cap this, it's not going to blow itself out anytime soon."

(Graph courtesy of Enviroknow.)