WASHINGTON - BP's estimate that only 5,000 barrels of oil are leaking daily from a well in the Gulf of Mexico, which the Obama administration hasn't disputed, could save the company millions of dollars in damages when the financial impact of the spill is resolved in court, legal experts say.

Greenpeace activists hoist a flag after climbing onto a balcony at BP headquarters in London May 20, 2010. (REUTERS/Stefan Wermuth) A month after a surge of gas from the undersea well engulfed the Deepwater Horizon offshore drilling rig in flames and triggered the massive leak that now threatens sea life, fisheries and tourist centers in five Gulf coast states, neither BP nor the federal government has tried to measure at the source the amount of crude pouring into the water.

BP and the Obama administration have said they don't want to take the measurements for fear of interfering with efforts to stop the leaks.

That decision, however, runs counter to BP's own regional plan for dealing with offshore leaks. "In the event of a significant release of oil," the 583-page plan says on Page 2, "an accurate estimation of the spill's total volume . . . is essential in providing preliminary data to plan and initiate cleanup operations."

Legal experts said that not having a credible official estimate of the leak's size provides another benefit for BP: The amount of oil spilled is certain to be key evidence in the court battles that are likely to result from the disaster. The size of the Exxon Valdez spill in Alaska, for example, was a significant factor that the jury considered when it assessed damages against Exxon.

"If they put off measuring, then it's going to be a battle of dueling experts after the fact trying to extrapolate how much spilled after it has all sunk or has been carried away," said Lloyd Benton Miller, one of the lead plaintiffs' lawyers in the Exxon Valdez spill litigation. "The ability to measure how much oil was released will be impossible."

"It's always a bottom-line issue," said Marilyn Heiman, a former Clinton administration Interior Department official who now heads the Arctic Program for the Pew Environment Group. "Any company wouldn't have an interest in having this kind of measurement if they can help it."

The size of the spill has become a high stakes political controversy that's put the Obama administration and the oil company on the defensive. In congressional testimony Wednesday, an engineering professor from Purdue University in West Lafayette, Ind., said that based on videos released Tuesday he estimated that the well was spewing at 95,000 barrels, or 4 million gallons, of oil a day into the gulf.

The Obama administration Thursday demanded that BP publicly release all information related to the disaster.

BP officials had pledged in congressional testimony to keep the public and government officials informed, Homeland Security Secretary Janet Napolitano and Environmental Protection Agency Administrator Lisa Jackson said in a letter to BP chief executive officer Tony Hayward.

"Those efforts, to date, have fallen short in both their scope and effectiveness," they wrote.

That letter came after members of Congress made similar demands of BP, leading to the release Tuesday of the new videos. One showed oil still billowing from one underwater pipe, despite an insertion tube BP now says is capturing 5,000 barrels of crude a day _ its entire initial estimate of the spill. The other showed a previously unseen leak spewing clouds of crude from just above the well's dysfunctional blowout preventer.

The EPA on Thursday ordered BP to switch to a less toxic version of the chemical mix it's using to disperse the oil. The EPA also for the first time posted on its website BP's test data of the dispersant's use in deep water. Those orders came days after McClatchy reported doubts about the dispersant's safety and members of Congress made a similar demand.

Scientists and environmentalists praised the government for demanding that more information be made public.

"This is exactly the role the government needs to be playing - they need to be overseeing BP's actions to assure that health and natural resources are protected, as much as possible, and that information is available to the public," said Gina Solomon, a senior scientist with the Natural Resources Defense Council.

This video, released Tuesday, shows billowing clouds of oil despite the presence of the insertion tube, visible to the right of the broken pipe

John Curry, a BP spokesman, said he hadn't seen the letter from Napolitano and Jackson and couldn't comment specifically, but added: "We're just trying to provide the information people are asking for at the same time we are trying to position a lot more resources to stop the flow of oil."

Curry offered no new estimate of how much oil is flowing from the leaks, but acknowledged that capturing 5,000 barrels of oil a day in the insertion tube is evidence that the official 5,000-barrel per day estimate is low.

"We've said at best it's a highly imprecise estimate," Curry said.

Curry said he knew of no efforts by BP to use its robotic equipment on the sea floor to measure the flow, but said that the efforts were entirely focused on containing the spill.

BP agreed Thursday to allow the posting of a live feed of the video of the oil spill, which lawmakers said would help scientists arrive at independent estimates of the spill.

"I'm sitting here looking at it right now, and it ain't 5,000 barrels a day, I'll guarantee it," said Bob Cavnar, a Houston engineer and blogger who's been involved in oil and gas exploration and production.

"In Houston, there's about 125,000, 150,000 engineers," he said. "And all the engineers can calculate what the flow is."

The feed eventually was overwhelmed by the number of people trying to view it and was removed from congressional websites.

This video, released Tuesday, provided the first public view of a second leak near the well's dysfunctional blowout preventer.

Calling the disaster site a "crime scene," Larry Schweiger, the president of the National Wildlife Federation, accused BP of a cover-up.

"BP cannot be left in charge of assessing the damage or controlling the data from their spill," Schweiger said. "The public deserves sound science, not sound bites from BP's CEO."

White House press secretary Robert Gibbs denied that the government was trying to cover up the size of the spill.

"The best and brightest minds in all of this government, and in the scientific community and in the world of commerce are focused on this problem. Everything that can be done is being done," he said.

Sens. Bill Nelson of Florida and Barbara Boxer of California, both Democrats, called on the Justice Department to investigate BP's drilling permits to determine whether the company had misled the government by claiming it had the technology needed to handle a big spill.

Since the spill, BP has announced five different approaches to sealing the leak. Three of those have been at least partially used: a 78-ton containment dome that failed; a small "top hat" dome that was placed on the seafloor May 11 but hasn't been used, and the insertion tube now siphoning a fraction of the spill. Of the two others, the "junk shot," which would fire shredded tires and debris into the damaged blowout preventer, is rarely mentioned, and the "top kill," which would force mud into the blowout preventer, may be tried this weekend.

National Oceanic and Atmospheric Administration head Jane Lubchenco told reporters on Thursday that a team of government scientists was assembled this week, a month after the spill began, to try to come up with a better estimate of the leak's volume.

She said the 5,000-barrel estimate was based on visual observations on the surface. "As the spill increased in size and began to break up it was no longer possible to use that effort, which is why we have shifted to using multiple paths to try to get at better estimates," she said.

Scientists have the instruments and the knowledge needed to figure out the flow rate, and several have complained publicly that they were turned down when they offered to help, as McClatchy reported Tuesday.

"The decision was made that the first priority had to be to stop the flow," Lubchenco said. Robotic vehicles were being used for that purpose and there was limited space for more of them to operate there at the same time, she said.

(Margaret Talev and David Lightman contributed to this article.)