OSLO -- The break-up of a leaking tanker off Spain may herald one of the world's worst oil spills, but experts say the distance to the coast and the warmth of the water may reduce the ecological devastation.

If the prestige lost all its 77,000 tons of fuel oil, it would rank 14th in world tanker spills, a list topped by the Atlantic Empress off Tobago in 1979 with 287,000 tons of oil.

It would be just ahead of the 74,000 tons of oil lost by the Aegean Sea which sank in 1992, also off northwest Spain.

"It's already a huge disaster -- thousands of fishermen are out of work, oil is coming onto beaches. This will also be one of the worst in terms of its impact," said Sian Pullen, head of the European Marine Programme at the World Wildlife Fund (WWF).

But she added that bacteria in the sea could help disperse the oil more quickly than, for instance, in the chillier waters of Alaska, where the Exxon Valdez ran aground in 1989, or the Erika disaster off northern France in December 1999, according to Reuters.

Also, the distance from land could help because the high seas will break up oil slicks before they reach beaches. "We're hopeful that we could see more oil break up than with the Erika, for instance," pullen said.

The stern section of the Bahamian-registered prestige sank on Tuesday 130 miles off northwest Spain, spilling 5,000-6,000 tons on top of about 5,000 tons spilt since its hull cracked last Wednesday. Its total load had been about 77,000 tons.

The battered bow section was expected to sink within hours.

The type of oil in the prestige could mute the impact of the spill -- experts said the fuel oil was of a lighter type than in the Erika, which spilt about 22,000 tons, and more refined than the crude in the Exxon Valdez, which spilt 34,000 tons.

"Some of the worst very heavy components will have been refined out," said David Santillo, a scientist with Greenpeace. "It all depends on the direction of the wind."

Braer Dispersed The Braer oil tanker grounded off Britain's Shetland islands in 1993, spilling 85,000 tons in the biggest tanker spill of the past decade. But it had a light crude that dispersed far more quickly that doomsayers predicted at the time, Reuters reported.

The impact of the Exxon Valdez, which ranks 20th by size in the spill ranking by the International Tanker Owners Pollution Federation (ITOPF) with 37,000 tons, was magnified because it was in a narrow sound in chill waters, Reuters reported.

Exxon spent two billion dollars cleaning up after the spill.

A decade after the Exxon Valdez, only bald eagles and river otters were considered as having recovered, Greenpeace said.

Harbour seals, cormorants, ducks and pigeon guillemots were still struggling in 1999.

In the worst case, the tanks on the prestige would implode from the pressure if both parts of the vessel sink in waters 3,600 metres (11,810 ft) deep.

If the tanks survive the sinking, oil would leak through the rusting metal in coming decades. marine life would be more able to adapt to such a slow-fuse time bomb than to a catastrophic spill. The depth of the water would make salvage impractical.

Hugh Parker, a technical manager at ITOPF, said there were examples of tankers sinking without rupturing their tanks.

Oil from the prestige is killing seabirds on Iberian beaches but will also kill fish in the high seas, even if much of the oil breaks up far from land. Small particles of oil can clog the gills of fish, suffocating them.

Whales and dolphins, which surface to breathe, have a better chance of swimming round slicks.

"These types of spill are happening because of our continued reliance on fossil fuels," Greenpeace's Santillo said.

Greenpeace wants far more stress on renewable energy and cuts in the use of fuels like oil and gas, blamed for global warming.