Since that day on 24 March 1989, the vessel's owner, Exxon, has spent dollars 2.5bn cleaning up. In October 1991, the company settled court cases by agreeing a further dollars 1bn to restore the Sound, coupled with a dollars 25m fine. But conservationists fear even this may not be enough.
'Superficially, it looks pretty good again,' Tony Turrini, of the National Wildlife Federation in Anchorage, said. 'But dig down, and there's lots of oil still there, while many of the wildlife populations have plummeted.'
Some good has come from the disaster. Government regulations now stipulate that US-built tankers must be double-hulled - one reason, say experts, why total spills in US waters have fallen dramatically. The 1991 total of 55,000 gallons (compared with 10.8 million released by the Exxon Valdez) was the lowest in 15 years. Vessel traffic systems have also been thoroughly overhauled.
Federal and Alaskan agencies know only too well that it was largely disorganisation among the rescue efforts that turned what could have been a containable spill into America's worst pollution disaster. A fresh accident, they insist, would draw a far more co- ordinated response.
But the harm to life in Prince William Sound still cannot be quantified. 'It's too early to tell the overall impact,' Bruce Mannheim, a lawyer for the Environment Defence Fund, said, 'but there was significant long-term damage to fish, sea-birds and marine mammals.'
A report last year by the US government's Oil Spill Trustee Council contrasted with the claims of an Exxon advertising campaign that the Sound's ecology had been fully restored, warning that the oil's effect was still working through spawning and breeding cycles.
In 1992, only 2 million pink salmon returned, compared to 8 million in a normal season. Between 3,500 and 5,500 sea otters were fatally poisoned, while 'thousands' of bald eagles, sea ducks, cormorants and other birds died.
There are subtler after-effects too. Eskimos on at least one island have been forced to turn from fishing to lumber to make a living, causing deforestation.
Key links in the food chain, such as mussels, are still contaminated; even the merits of 'bio-remediation' - the release of natural microbes to eat up contaminants - are contested.
Theoretically, Exxon's dollars 1bn should make a big difference. But Mr Mannheim warned: 'There is quite a debate whether it is actually being spent on the ground, or being frittered away on studies by research groups and the like.'