NEW YORK (CNNMoney.com) -- Coast Guard officials are considering setting the Gulf of Mexico oil slick on fire as it moved Tuesday to within 20 miles of sensitive ecological areas in the Mississippi River Delta.
Officials say it could become one of worst spills in U.S. history.
Oil is still leaking at a rate of about 42,000 gallons a day from the well, located some 50 miles off the coast of Louisiana beneath a drill rig that exploded and sank last week. Eleven workers are still missing following the incident, and are presumed dead.
BP, the well's owner, is racing to shut off the well using eight remote controlled submarines, but has had no luck as of yet.
"If we don't secure the well, this could be one of the most serious oil spills in U.S. history," Coast Guard Rear Admiral Mary Landry, head of a joint response task force, said at a press conference Tuesday afternoon.
Twenty miles is the closest the slick has come to land so far.
Officials said oil slicks are sometimes set on fire, especially when they are near sensitive marsh areas where heavy equipment used to clean the oil may cause more harm than good.
If the slick is set on fire, it would be a controlled burn using fire-proof booms, and only done during the day, said Landry. It could begin as early as Wednesday.
The spill, measured from end to end, stretched as wide as 42 miles by 80 miles, although oil isn't necessarily covering that entire area.
Most of the slick is a thin sheen on the water's surface, ranging in thickness from a couple of molecules to the equivalent of a layer of paint. About 3% of it is a heavy, pudding-like crude oil.
At its current flow rate would take over 260 days to rival the Exxon Valdez disaster, which discharged some 11 million gallons into Alaska's Price William Sound. Still, even if it never compares to the Exxon Valdes spill's size, if it makes landfall it'll have serious ecological repercussions.
The Coast Guard, BP, and the rig's owner Transocean (RIG), have deployed nearly 50 vessels to help contain and clean the slick.
Marine life has been spotted in the area. Over the weekend a plane from the U.S. Fish and Wildlife Service sighted five small whales nearby. Crews working to contain the spill were alerted to their presence.
Efforts are also underway near the shoreline to deal with the spill should it reach land, including positioning boom material around sensitive ecological areas.
Five staging areas have been set up on land, stretching from Venice, La. to Pensacola, Fla.
Landry said it appears the slick should remain at sea for at least the next three days, although weather reports for the latter part of that period suggest the wind could shift and blow the slick toward land.
The oil, if it stays at sea, will eventually evaporate, breakdown and sink, or get cleaned up.
But analysts have said the spill could have political fallout, especially if it reaches shore.
Several lawmakers and interest groups have led a charge over the last several years to open up more parts of the U.S. coast for oil drilling, efforts that are generally supported by the public.
That support could erode if crude oil starts washing up on the Louisiana or Mississippi coasts.
The well is expected to continue leaking until it is sealed. The leak appears to be coming from a pipe that ran from the well head to the drilling rig, which is now laying upside down in 5,000 feet of water not far from the well head.
It has not been decided if the rig will be salvaged or remain where it is, a Transocean official said Monday.
To seal the leak, three approaches are being tried.
BP is now using a set of remote controlled submarines in an attempt to activate the well's "blow out preventer" -- a steel device the size of a small house that sits atop the well and is intended to choke off the flow of oil in the event of a disaster.
It's not clear why that device didn't not originally act to cap the well, or if it will be of any use going forward.
BP (BP) is also bringing in another drilling rig which could seal the well, but that effort will take months, according to a BP spokesman.
In the meantime, the company is also trying a novel approach to capture the oil -- using a dome right above the well head. The dome resembles an inverted funnel, with a pipe leading up to ships waiting at the surface to capture the oil. That tactic has never been tried in water this deep.
A BP spokesman said the dome should be ready in two to four weeks.
The blast last week, which is still under investigation, resulted in 11 workers going missing. The search for them was suspended last Friday.
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