NEW ORLEANS - Researchers tracking the massive oil spill in the Gulf of Mexico say computer models show the black ooze may have already entered a major current flowing towards Florida and the Atlantic Ocean.

A research vessel has been sent out to learn more.

William Hogarth, dean of the University of South Florida's College of Marine Science, told The Associated Press today that one model shows that the oil has already entered the loop current, which is the largest in the Gulf.

The model is based on weather, ocean current and spill data from the US Navy and the National Oceanic and Atmospheric Administration, among other sources.

Hogarth said a second model shows the oil is about 5km from the current - still dangerously close.

The current flows in a looping pattern in the Gulf, through the area where the blown-out well is, east to the Florida Keys National Marine Sanctuary.

The ecological disaster, now nearing a month old, started when BP's Deepwater Horizon oil platform exploded and disintegrated on April 20.

The Gulf of Mexico oil spill may actually be many times larger than realised, with vast amounts of oil spilling out in deep undersea "plumes" which cannot be seen from the surface, scientists suggested today, in a development which put yet more pressure on Britain's oil giant BP to cap the leaking well as soon as possible.

BP is trying to stem the flow by threading a tube into the leak to siphon the oil to a tanker on the surface, in the third separate attempt the company has made to halt the "gusher" on the sea floor, nearly 1.6km down. It had failed to halt it with huge blowout preventers on the well, or by putting a 100-ton box above the flow to trap and siphon it to the surface.

After trying and failing on Saturday, engineers this morning succeeded in fitting the tube into a broken sea-floor pipe using remotely-controlled robot submarines. The four-inch wide tube was inserted into a leaking riser, from which most of the flow of oil is coming. If it works, it could siphon a substantial amount of the oil leaking from the damaged well into barges and tankers.

But as BP struggled to cap the well. the company's troubles increased with the news that the flow rate from the ruptured Deepwater Horizon drilling rig, which the US government calculated from satellite imagery to be about 5,000 barrels of oil a day, and which BP has gone along with, may actually be between 25,000 and 80,000 barrels per day (bpd), American researchers now believe (one tonne of crude equals 7.33 barrels, or 308 gallons.

The oil escaping from the rig, which BP had leased from the Swiss-based drilling company Transocean, is already threatening an environmental and economic catastrophe along the Gulf coast.

But it could be much worse than so far anticipated. If the oil were flowing at the 80,000 bpd top rate now envisaged, unseen beneath the giant oil slick on the surface, the amount which has escaped since the accident would be more than two million barrels in total, which would make it the fourth worst marine oil-spill in history.

If the well cannot be capped from above and the leak can be stopped only by drilling a relief well, which has already begun but will take three months, the amount of oil leaked might amount to more than five million barrels. In June 1979, 3.5 million barrels escaped from the Mexican Ixtoc 1 well, also in the Gulf, after a blowout. Ixtoc 1 took nine months to cap.

The biggest oil-spill was deliberate, when valves at the Sea Island oil terminal in Kuwait were opened by Iraqi forces at the end of the Gulf War in January 1991, which is thought to have released more than 10 million barrels of oil into the Persian Gulf.

The new leakage rate assessment from Deepwater Horizon has come from scientists from several universities on board the US research vessel Pelican. Their key finding has been that there are enormous plumes of oil hanging in the deep water, one of which is 10 miles long, three miles wide and up to 300ft thick.

"There's a shocking amount of oil in the deep water, relative to what you see in the surface water," said Dr Mandy Joye, of the Department of Marine Science at the University of Georgia, who is co-ordinating the mission from her laboratory in Athens, Georgia. "There's a tremendous amount of oil in multiple layers, three or four or five layers deep in the water column."

The shallowest oil plume the group detected was at 2,300ft and the deepest was near the sea-floor at 4,200ft. The scientists are alarmed that the underwater plumes are depleting the dissolved oxygen in the seawater. The oxygen had already dropped by 30 per cent near some of the plumes, said Dr Joye.

"If you keep those kinds of rates up, you could draw the oxygen down to very low levels that are dangerous to animals in a couple of months. It could take years, possibly decades, for the system to recover from an infusion of this quantity of oil and gas. We've never seen anything like this before. It's impossible to fathom the impact."

BP, the largest oil and gas producer in the US, which under US law is responsible for tackling the disaster and the subsequent clean-up, is coming under ever-increasing pressure over the length of time it is taking to stop the oil flowing, now nearly a month.

The Obama administration is seeking "immediate public clarification" from Tony Hayward, BP's chief executive, over the company's intentions about paying the costs associated with the spill. "The public has a right to a clear understanding of BP's commitment to redress all the damage that has occurred or that will occur in the future as a result of the spill," Ken Salazar, the US Interior Secretary, said at the weekend.

Paddy Power, the online bookmaker, has Mr Hayward, who was thought to be the answer to all the company's problems when he succeeded John Browne as CEO in 2007, at only 8/11 to survive the year.

- INDEPENDENT, AP