Thousands of tons of heavy fuel remain in the bow and stern sections of the Prestige, the oil tanker that split in half off the northwestern coast of Spain on November 19, 2002. It sank to the seabed, more than 3,500 meters deep in the Atlantic Ocean some 200 kilometers from Galicia. Tons of toxic fuel have oozed from 20 cracks in the hulls as semisolid black strings, like toothpaste being squeezed from a tube, and have drifted toward the sea surface. It has become Spain's worst ecological disaster ever, halting coastal fishing and polluting beaches. The ship has already spilled at least 30,000 tons of oil, and researchers aren't sure when the seepage will stop.

At first, scientists thought that the fuel would freeze: oil remains fluid to six degrees Celsius, and the deep water around the wreck is at 2.75 degrees C. Experts guess that the Prestige left port from Ventspils, Latvia, in the Baltic Sea with 77,000 tons at 50 degrees C. But no one knows what the oil temperature is now. According to Malcolm L. Spaulding, professor of ocean engineering at the University of Rhode Island, the calculations of the cooling time for the oil in the bow and the stern, which lie 2.5 kilometers apart on the seafloor, have proved extraordinarily difficult. In principle, the fuel in contact with the external walls of the hulls should cool faster than that in the center of the tank. The time it takes for all the oil to cool down depends on the amount and rate of mixing, a critical factor "that complicates heat transfer from the oil to the tank walls and finally to the seawater," Spaulding explains. If the oil mixed together well, the entire cargo should have cooled off and frozen in 40 days. That did not happen, Spaulding remarks, probably because the mixing is substantially reduced. He now anticipates "cooling times of many months to several years."

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