The report said corrosion would mean the complete disintegration of the tanker over a period of up to 40 years. More than 50,000 tonnes of oil are estimated to be still inside the sunken ship's tanks.

"We can conclude that, even if the holes were completely sealed, structural deterioration (means that)...the leakage of oil from the tanks cannot be avoided," a committee from Spain's Scientific Investigation Centre concluded.

The French mini-submarine Nautile has been patching up cracks and collecting snakes of leaking oil in buckets from the hull since late December.

However, Spanish Deputy Prime Minister Mariano Rajoy said this week that scientists hoped to provide a definitive solution to the problem of the Prestige soon.

"In the first fortnight of February, (scientists) will tell us what the definitive solution is, and it can be carried out in the summer," Rajoy told Tele Cinco television.

Thick, tar-like oil has been leaking from the Prestige and washing up on beaches over a large area of northern Spain and on stretches of France's Atlantic coast since the 26-year-old tanker sank, devastating some of Spain's prime fishing grounds.

Holes in the wreck's hull are being sealed in an attempt to keep the remaining oil in place until some kind of permanent solution can be found.