WASHINGTON — BP recovered 18,600 barrels of oil from its gushing Deepwater Horizon well on Wednesday, the most so far, but still just a fraction of what is spewing into the Gulf of Mexico.

The amount underscores how wrong early estimates of the spill's size were and serves as a reminder of the weeks-long reluctance of both BP and the Obama administration to recognize the full extent of the disaster, which began April 20 when the Deepwater Horizon drilling rig was enveloped in methane gas from the well and burst into flames. It sank two days later.

Earlier this week, Energy Secretary Steven Chu said that a panel of experts had pegged the leak's size at 35,000 to 60,000 barrels a day — and that may still be low, he cautioned.

That estimate, however, was only the latest in a series that began at 1,000 barrels a day, then held at 5,000 barrels a day until May 27, when a government-convened Flow Rate Technical Group came up with two estimates. One of those, 12,000 to 19,000, was frequently cited by Obama administration officials, including White House adviser Carol Browner and Coast Guard Adm. Thad Allen, while the other, of at least 12,000 to 25,000 barrels, with no maximum estimate possible, was rarely brought up.

Marcia McNutt, the head of the U.S. Geological Survey, announced a new estimate on June 10 — 20,000 to 40,000 barrels, and possibly more, a figure that was overtaken just five days later by Chu's announcement Tuesday.

Video from the well site on Thursday showed no apparent decrease in the amount of oil spewing from the well despite the higher collection rate, and a group of seven senators asked U.S. Atty. Gen. Eric Holder to open a criminal invesitgation into whether BP intentionally underestimated the size of the spill to avoid hundreds of millions, if not billions, of dollars in fines.

"If BP is shown to have misled the government in estimating the size of the spill, it may have compromised response efforts," the senators said in a letter to Holder. The letter was signed by Sens. Ronbert Menendez, D-N.J., Charles Schumer, D-NY, Patty Murray, D-Wash., Frank Lautenberg, D-N.J., Kirsten Gillibrand, D-N.Y., Bill Nelson, D-Fla., and Sheldon Whitehouse, D-R.I.

BP said approximately 14,750 barrels of the oil collected Wednesday went to the Discoverer Enterprise drill ship, which is drawing oil through a "top hat" containment device placed atop the well's failed blowout preventer on June 3. Another 3,850 barrels were taken aboard the Q4000 drilling platform through hoses leading directly to the blowout preventer and was then burned, BP said.

BP has said it expects the Q4000 to recover as much as 10,000 barrels a day, all of which will be burned. BP and Coast Guard officials have said the Discoverer Enterprise has the capacity to collect as much as 18,000 barrels a day, but it has yet to collect that amount; the highest one-day total was 15,800 barrels, on June 9.

BP hopes to add a third recovery vessel by the end of June and raise the amount of oil collected to between 40,000 and 53,000 barrels a day.