HOUSTON, (Reuters) – U.S. government scientists yesterday doubled their estimate of the amount of oil gushing  out of a ruptured Gulf of Mexico oil well as British energy  giant BP scrambled to stem the leak.

The news that the flow rate may be as high 40,000 barrels  (1.68 million gallons/6.36 million liters) per day came after  U.S. markets closed.

BP shares closed 6.65 percent down in London at 365.50  pence while in New York they rebounded from 14-year lows to end  12.3 percent higher at $32.78.

Yesterday the White House said that President Barack  Obama and senior administration officials would meet BP  Chairman Carl-Henric Svanberg next Wednesday.

BP has come under increased pressure from the Obama  administration in recent days and on Thursday British Prime  Minister David Cameron said Britain stood ready to help the  British company deal with the spill.

Speaking during a visit to Afghanistan, Cameron said he  would take up the matter Obama when they speak in the next few  days.

Neighboring Mexico also entered the fray yesterday. It  expects oil from BP Plc’s damaged Gulf of Mexico well to reach  its shores by December, and is considering how to sue the  company for any environmental damage, Mexico’s environment  minister told Reuters.

Environment Minister Juan Elvira said Mexico is trying to  stock up on oil booms and netting, a tough task because the  United States has used up most of the gear available to protect  its coastline, to try to capture oil that will start drifting  south when sea currents change in October.

The spill, already the worst in U.S. history, may well be  much bigger than many had thought.     U.S. scientists said yesterday that between 20,000 and  40,000 barrels (840,000 and 1.7 million gallons/3.2 million and  6.4 million litres) of oil flowed from the well before June 3,  when BP’s remotely operated robots sawed through an underwater  pipe to clear the way for a capping procedure.

The cutting of the pipe likely increased the flow, but BP  says it has collected 73,324 barrels (3.1 million gallons/11,7  million litres) of oil since installing the capping system.

The well’s average flow rate was 25,000-30,000 bpd,  according to the findings of the so-called Flow Rate Technical  Group announced by U.S. Geological Survey Director Marcia  McNutt.

BP had no input into the team’s findings.

The wide variation in the estimates points to the  difficulty in estimating flow of a well that is 1 mile (1.6 km)  beneath the surface and reachable only by remotely operated  robots.

BP said it was capturing more of the torrent of oil that  has spewed relentlessly from the sea bottom since the April 20  rig explosion that killed 11 workers and set the disaster in  motion.

But the almost 16,000 barrels it said on Thursday it had  collected in the previous 24 hours is triple its initial  estimates of the leak’s flow rate, a point that will not be  lost on critics as U.S. public and political anger mount.