Storm clouds form near a BP station in Alexandria, Virginia July 19, 2010. REUTERS/Molly Riley 

A hard hat from an oil worker lies in oil from the Deepwater Horizon oil spill on East Grand Terre Island, Louisiana June 8, 2010. Energy giant BP Plc said on Tuesday it had sharply increased the amount of oil it was capturing from its blown-out Gulf of Mexico well, but U.S. officials want to know exactly how much oil is still gushing out. REUTERS/Lee Celano 

Journalists and members of the Louisiana Wildlife Federation stand on a sand bank in Breton Island as oil leaking from the Deepwater Horizon wellhead continues to spread in the Gulf of Mexico, May 3, 2010. Energy giant BP Plc was under siege on Monday over the catastrophic oil spill from its ruptured Gulf of Mexico well, as its shares fell and the U.S. government pressed it to try to limit a major environmental disaster. As a huge oil slick advanced toward the Gulf Coast shoreline, the London-based company came under increasing pressure to do more to stop, or at least control, what is fast turning into the worst oil spillage in U.S. history. REUTERS/Carlos Barria 

A protective boom is seen as oil from the Deepwater Horizon spill recedes back into the Gulf of Mexico after washing into a drainage canal in Waveland, Mississippi July 7, 2010. REUTERS/Lee Celano 

EDF (Environmental Defense Fund) coastal scientist Angelina Freeman takes a sample of oil while surveying the conditions of Bartaria Bay near Venice, Louisiana June 6, 2010. Oil from BP's out-of-control Gulf of Mexico oil spill could threaten the Mississippi and Alabama coasts this week, U.S. forecasters said, as public anger surged over the nation's worst environmental disaster. REUTERS/Sean Gardner 

BP CEO Tony Hayward walks past protesters as he arrives to testify about the BP oil spill in the Gulf of Mexico at the House Energy and Commerce Committee on Capitol Hill, June 17, 2010. REUTERS/Larry Downing 

Work crews on boats gather to clean marshland impacted by oil from the Deepwater Horizon Spill near Bay Jimmy, in the Barataria Bay of Louisiana June 17, 2010. REUTERS/Lee Celano 

Oil from the Deepwater Horizon oil spill swirls in various colours in shallow water on East Grand Terre Island, Louisiana June 8, 2010. Energy giant BP Plc said on Tuesday it had sharply increased the amount of oil it was capturing from its blown-out Gulf of Mexico well, but U.S. officials want to know exactly how much oil is still gushing out. REUTERS/Lee Celano 

Beach goers sunbathe behind a wall of hay bales, used to absorb any oil that might come ashore, on Dauphin Island, Alabama May 11, 2010. Oil workers, volunteers and the military have been battling to shut off a gushing oil leak in the Gulf of Mexico and stop the huge spreading slick from reaching major ports, tourist beaches, wildlife refuges and fishing grounds. REUTERS/Brian Snyder 

A Northern Gannet seabird, affected by the BP oil spill in the Gulf of Mexico, is cleaned by rehabilitators at a rescue center facility set up by the International Bird Rescue Research Center (IBRRC) in Fort Jackson, Louisiana July 1, 2010. REUTERS/Sean Gardner 

U.S. President Barack Obama surveys damage along the Louisiana coastline at Fourchon Beach caused after a BP oil line ruptured in the Gulf of Mexico, May 28, 2010. REUTERS/Larry Downing 

Smoke billows from a controlled burn of spilled oil off the Louisiana coast in the Gulf of Mexico coast line June 13, 2010. Millions of gallons of oil have poured into the Gulf since an April 20 explosion on an offshore rig killed 11 workers and ruptured BP's deep-sea well. REUTERS/Sean Gardner 

Members of the U.S. Army National Guard's 711 Brigade Support Battalion erect Hesco barriers to potentially stop any oil from damaging Dauphin Island, Alabama May 5, 2010. Oil spill workers raced against time in the Gulf of Mexico on Wednesday, hoping to take advantage of another day of calm seas in their fight to contain a huge spreading oil slick before it hits the U.S. shoreline. REUTERS/Brian Snyder