Most large oil spills in history stemmed from tanker accidents, and their sizes could be reckoned based on the holding capacity of the wrecked vessels.
Oil company BP, which owns the leaking well, provided the original estimate of a thousand barrels a day, based on underwater cameras that recorded the flow from leaks 5,000 feet (1,524 meters) below water. (See oil rig pictures.)
But the U.S. National Oceanic and Atmospheric Administration, or NOAA, which has also been monitoring the disaster on the scene and from the air, now says evidence points to the spill being five times worse—about 5,000 barrels a day. BP says it has identified a potentially new leak in the damaged pipes on the sea floor, which it had not seen before.
Photograph by Chris Graythen, Getty Images
Gulf Oil Colors
Both the size and color of the oil slick on the water's surface are indicators of how much oil has actually flowed into the Gulf of Mexico so far, said Doug Helton, incident operations coordinator for NOAA.
A silver-grey sheen or rainbow color, as seen in the above picture taken Wednesday, indicates a thin sheet of oil—perhaps only a molecule wide, he said. Authorities have said that the majority of oil seen on the surface of the Gulf—well over 90 percent—is spread out into such a thin layer. (See a picture of the silvery oil spill taken by a NASA satellite.)
But dark black patches indicate that thick pools of oil lie beneath—as much as five barrels-worth of oil per acre (0.4 hectare) in the darkest areas. The extent of dark patches seen in the Gulf led NOAA observers to believe that previous flow estimates were too conservative, Helton said. The size of the spill now covers several thousand square miles.
Photograph by Chris Graythen, Getty Images
Gulf Oil Spill's Spread
A satellite picture taken Monday captures a small plane flying over rust-colored "streamers" of crude oil visible on the surface of the Gulf.
Burning will work only when the oil can be gathered into a certain thickness in long, tubelike, fireproof booms. Although tests have shown such burning can remove 50 to 90 percent of the oil that can be collected in this manner, it's not known if enough of the oil from the Deepwater Horizon rig spill can be rounded up at one time. (See a map of the Gulf of Mexico oil spill.)
Image by DigitalGlobe via Getty Images
Gulf's Dark Oil "Stains"
Dark splotches dot the thin sheen of oil seen on the Gulf's surface near New Orleans on Wednesday. Models show that oil escaping from damaged pipes on the seafloor may take three hours to rise the 5,000 feet (1,524 meters) to the water's surface, said NOAA incident operations coordinator Helton.
Because oil is buoyant, scientists expect anything that leaks from the pipes to come to the surface. But how fast the oil moves depends on the size of the globules that form. Under the enormous pressure of deep water, small globs rise more slowly than large ones.
A "river" of crude oil drifts across the Gulf's surface, as seen in an aerial picture taken Wednesday.
The weather has complicated efforts to fight the Gulf oil spill, noted members of the federal-industry joint task force. Choppy seas are making it difficult to deploy skimming vessels and to attempt controlled burns of the oil. More than 98,000 gallons (370,970 liters) of chemical dispersant have been dropped on the oil. The dispersant does not actually reduce the total amount of oil entering the environment, but changes the chemical and physical properties of the oil. This makes the oil more likely to mix into the water column than to contaminate the shoreline.
The European Space Agency's Envisat orbiter snapped this picture of the Gulf oil spill last Thursday, seen as a dark swirl not far from the Louisiana coast.
Winds from the south have been driving the oil spill closer to land all week. The federal-industry joint response team projects that the leading edge of the oil plume will reach the Mississippi River Delta and the barrier islands of Louisiana by Friday night.
The area includes the Delta National Wildlife Refuge, where lush, marshy vegetation provides a winter stopover for hundreds of thousands of migrating snow geese, coots, and ducks. The wetlands refuge is also home to numerous endangered species, including American alligators, brown pelicans, peregrine falcons, and piping plovers.
Wildlife protection officials are trying the strategy of "hazing," or using loud propane-fired cannons, to chase birds from the water's edge.