A boat uses a boom and absorbent material to soak up oil in Cat Bay, near Grand Isle, La., on June 28. A tropical storm is expected to hit the Gulf and impede cleanup efforts.
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Florida Gov. Charlie Crist and wife Carole Rome Crist (right) stand with others during a Hands Across the Sand event June 26 in Pensacola, Fla. The event was staged across the nation to protest offshore oil drilling.
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Oil clouds the surface of Barataria Bay near Port Sulpher, La., on June 19.
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Workers adjust piping while drilling a relief well at the site of the Deepwater Horizon oil spill.
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A dolphin rises up out of the water near Grand Terre Island off the coast of Louisiana on June 14.
Derick E. Hingle/AP
President Obama stands with Mississippi Gov. Haley Barbour (right) and Gulfport, Miss., Mayor George Schloegel after meeting with residents affected by the oil spill.
Crude oil washes ashore in Orange Beach, Ala., on June 12. Oil slicks, 4 to 6 inches thick in some parts, have washed up along the Alabama coast.
A volunteer uses a toothbrush to clean an oil-covered white pelican at the Fort Jackson Oiled Wildlife Rehabilitation Center in Buras, La., June 9.
Saul Loeb/AFP/Getty Images
A shrimp boat skims oil from the surface of the water just off Orange Beach, Ala., as a family enjoys the surf. Oily tar balls have started washing up on Orange Beach and beaches in the western Florida panhandle.
Sand from a dredge is pumped onto East Grand Terre Island, La., to provide a barrier against the Deepwater Horizon oil spill, June 8.
A dead turtle floats on a pool of oil from the Deepwater Horizon spill in Barataria Bay off the coast of Louisiana on June 7.
Workers use absorbent pads to remove oil that has washed ashore from the spill in Grand Isle, La., June 6.
Plaquemines Parish coastal zone director P.J. Hahn lifts an oil-covered pelican out of the water on Queen Bess Island in Plaquemines Parish, La., June 5.
Heavy oil pools along the side of a boom just outside Cat Island in Grand Isle, La., June 6.
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President Obama walks alongside Grand Isle Mayor David Camardelle (from right), U.S. Coast Guard Adm. Thad Allen, who is in charge of the federal response to the spill, and Chris Camardelle after meeting with local business owners in Grand Isle, La., June 4.
Saul Loeb/AFP/Getty Images
A brown pelican sits on the beach at East Grand Terre Island along the Louisiana coast after being drenched in oil from the BP Deepwater Horizon oil spill, June 3.
U.S. Attorney General Eric Holder announces that the Justice Department has launched a criminal investigation into the BP oil spill. With him, from left: Stephanie Finley and Jim Letten, U.S. attorneys for the Western District of Louisiana; Ignacia Moreno, assistant attorney general for the Environment and Natural Resources Division; Tony West, assistant attorney general, Civil Division; and Don Burkhalter, U.S. attorney for the Southern District of Mississippi.
The oil slick off the coast of Louisiana, seen from above.
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A worker leaves the beach in Grand Isle, La., on May 30. BP is turning to yet another mix of undersea robot maneuvers to help keep more crude oil from flowing into the Gulf.
Jae C. Hong/AP
Protesters cover themselves with a water and paint mixture during a demonstration at a BP gas station in New York City on May 28.
Workers clean up oil in Pass a Loutre, La. The latest attempt to plug the leak was unsuccessful.
Jae C. Hong, File/AP
Residents listen to a discussion with parish officials and a BP representative on May 25 in Chalmette, La. Officials now say that it may be impossible to clean the hundreds of miles of coastal wetlands affected by the massive oil spill.
Sean Gardner/Getty Images
An oil-soaked pelican takes flight after Louisiana Fish and Wildlife employees tried to corral it on an island in Barataria Bay on the coast of Louisiana. The island, which is home to hundreds of brown pelican nests as well at terns, gulls and roseate spoonbills, is impacted by oil from the Deepwater Horizon spill.
A sign warns the public to stay away from the beach on Grand Isle, La. Officials closed the oil-covered beaches to the public indefinitely on Saturday.
John Moore/Getty Images
Pelican eggs stained with oil sit in a nest on an island in Barataria Bay on May 22.
A bird flies over oil that has collected on wetlands on Elmer's Island in Grand Isle, La., May 20. The oil came inland despite oil booms that were placed at the wetlands' mouth on the Gulf of Mexico.
Members of the Louisiana National Guard build a land bridge at the mouth of wetlands on Elmer's Island.
The hands of boat captain Preston Morris are covered in oil after collecting surface samples from the marsh of Pass a Loutre, La., on May 19.
Louisiana Gov. Bobby Jindal (center) and Plaquemines Parish President Billy Nungesser (right) tour the oil-impacted marsh of Pass a Loutre, La. "This is the heavy oil that everyone's been fearing that is here now," said Jindal.
BP Chairman and President Lamar McKay (left), with Transocean President and CEO Steven Newman (center) and Applied Science Associates Principal Deborah French McCay, testifies during a Senate Committee on Commerce, Science, and Transportation hearing May 18 on response efforts to the Gulf Coast oil spill.
Manuel Balce Ceneta/AP
This undated frame grab image received from BP and provided by the Senate Environment and Public Works Committee shows details of the oil spill in the Gulf of Mexico. BP has agreed to display a live video feed of the oil gusher on the Select Committee on Energy Independence and Global Warming Committee's website beginning Thursday evening.
Senate Environment and Public Works Committee/AP
President Obama speaks with local fishermen about how they are affected by the oil spill in Venice, La., on May 2.
Saul Loeb/AFP/Getty Images
Danene Birtell with Tri-State Bird Rescue and Research tends to a Northern Gannet in Fort Jackson, La., on April 30. The bird, normally white when full grown, is covered in oil from the oil spill.
Since the explosion, a third oil leak has been discovered in the blown-out well.
In this aerial photo taken April 21 more than 50 miles southeast of Venice, La., the Deepwater Horizon oil rig burns.
Tendrils of oil mar the waters of the Gulf of Mexico in this satellite image taken Monday. An estimated 5,000 barrels of oil a day are seeping into the Gulf, after an explosion last week on a drilling rig about 50 miles off the Louisiana coast.
Courtesy of Digital Globe
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The tan color indicates the trajectory of the oil spill for April 30.
An oil spill that threatened to eclipse even the Exxon Valdez disaster spread out of control and drifted inexorably toward the Gulf Coast as fishermen rushed to scoop up shrimp and crews spread floating barriers around marshes.
The spill was both bigger and closer than imagined — five times larger than first estimated, with the leading edge just 3 miles from the Louisiana shore.
"It is of grave concern," David Kennedy of the National Oceanic and Atmospheric Administration, told The Associated Press.
"I am frightened. This is a very, very big thing. And the efforts that are going to be required to do anything about it, especially if it continues on, are just mind-boggling."
The oil slick could become the nation's worst environmental disaster in decades, threatening hundreds of species of fish, birds and other wildlife along the Gulf Coast, one of the world's richest seafood grounds, teeming with shrimp, oysters and other marine life.
Louisiana Gov. Bobby Jindal declared a state of emergency Thursday, and President Obama pledged his administration will use "every single resource at our disposal."
Jindal made the declaration shortly after Homeland Security Secretary Janet Napolitano called the disaster a "spill of national significance."
The Coast Guard worked with BP, which operated the oil rig that exploded and sank last week, to deploy floating booms, skimmers and chemical dispersants, and set controlled fires to burn the oil off the water's surface. Obama said the response could include the Defense Department.
Thursday's order allows the state to free up resources to begin preparing for the oil to reach the shore.
Napolitano, Interior Secretary Ken Salazar and environmental protection administrator Lisa Jackson will travel Friday to the Gulf of Mexico to oversee efforts to contain the spill. White House press secretary Robert Gibbs said the administration also may send military ships and personnel to help control damage from the spill.
British oil giant BP confirmed Thursday that up to 5,000 barrels, or 200,000 gallons, of oil a day are spilling from the site of the deadly oil rig explosion.
At that rate, the spill could easily eclipse the worst oil spill in U.S. history — the 11 million gallons that leaked from the grounded tanker Exxon Valdez in Alaska's Prince William Sound in 1989 — in the three months it could take to drill a relief well and plug the gushing well 5,000 feet underwater on the seafloor. Ultimately, the spill could grow much larger than the Valdez because Gulf of Mexico wells typically hold many times more oil than a single tanker.
Jackie Savitz, a toxicology scientist with the environmental group Oceani, says that at the current flow rate, the spill will reach the 11 million gallon mark of the Exxon Valdez spill in 50 days. The Gulf holds several endangered and threatened species, including four species of endangered sea turtle, in addition to dolphins, porpoises and whales.
"This is one of only two spawning areas for bluefin tuna in the world," Savitz said. "If larvae are exposed, there's a good chance they won't survive or their survival will be reduced because of the oil spill."
Doug Suttles, the oil company's chief operating officer, told NBC's Today show that oil is bubbling up from the ocean bottom at a rate of 1,000 to 5,000 barrels a day. He said the company would welcome help from the U.S. Defense Department and other agencies in containing the slick.
"We'll take help from anyone," Suttles said.
As the slick has grown, so have potential cleanup costs.
"As the president and the law have made clear, BP is the responsible party" for costs, Napolitano said.
A third leak was discovered in the blown-out well, which is about a mile under water. Coast Guard Rear Adm. Mary Landry said it may be time for government agencies to offer up "technologies that may surpass abilities of the private sector" to get the slick under control.
Landry said more than 5,000 barrels a day of sweet crude are discharging into the gulf, not the 1,000 barrels officials had estimated for days since the Deepwater Horizon drilling rig exploded and sank 50 miles off the Louisiana Coast. The new oil spill estimate came from the federal National Oceanic Atmospheric Administration.
Initially, Suttles said he did not believe the amount of oil spilling into the water was greater than earlier estimates. But on Thursday, he acknowledged that the leak may be as high as the government is estimating.
"Using the satellite imagery and our overflights, we can now say it looks like it's more than a thousand. It's a range" of up to 5,000, he said.
BP spokesman John Curry said it doesn't really matter what the numbers are, the slick is what it is, and corralling it is the important thing.
"We can't physically go down and put a meter on the leak to measure how much is flowing, so it's all a guess, it's all an estimate," he said. "And the different estimates don't change our response. I mean, they all are within the general range of uncertainty, and we're not going to stop until we get this done."
Eleven workers are missing and presumed dead, and more than 100 escaped the blast, the cause of which has not been determined.
Industry officials say replacing the Deepwater Horizon, owned by Transocean Ltd. and operated by BP, would cost up to $700 million. BP has said its costs for containing the spill are running at $6 million a day. The company said it will spend $100 million to drill the relief well. The Coast Guard has not yet reported its expenses.
Material from NPR's Wade Goodwyn and The Associated Press was used in this report.