Minutes after midnight, on March 24, 1989, the supertanker Exxon Valdez ran aground on Bligh Reef in Prince William Sound on Alaska's southern coast. Some 10.8 million gallons (40,900 kiloliters) of oil spilled from the deep gash in the ship's hull, eventually washing up on more than 1,200 miles (1,900 kilometers) of pristine coastline, causing what still stands as the worst oil spill in U.S. history.

Slide Show: Preventing Another Exxon Valdez Disaster

The impact on local wildlife was devastating: An estimated 250,000 seabirds died in the months after the spill, and 14 members of the 36 local Prince William Sound killer whale pod had disappeared by 1990. The so-called carcass count also tallied, among other creatures, 1,000 dead sea otters as well as 151 dead bald eagles, according to the Exxon Valdez Oil Spill Trustee Council (EVOSTC), a group formed to oversee restoration projects. Some of the spill remains to this day, with a 2003 estimate pointing to about 20,000 gallons (75,700 liters) soaked deep into sands in intertidal zones, slowly poisoning ducks and other shore creatures.

The spill affected people living in or near the sound economically and culturally. Commercial fishing and tourism both took hits; pre-spill levels of herring, a fish important for marine food chains and human consumption have yet to bounce back. Alaskan Native communities that subsist on fish and shellfish in the region only saw some of the dwindled sea life populations regain their pre-spill levels by 2003.

The Exxon Valdez calamity also incurred crushing cleanup costs and a legal maelstrom. The giant energy company, then known as Exxon (and as ExxonMobil since its 1999 merger with Mobil) initially settled for $900 million in 1991, to be paid over ten years. Then, in 1994, a jury in Alaska ordered Exxon to pay an additional $5 billion in punitive damages as a result of a class-action lawsuit brought by thousands of Alaskan residents. Just last year, however, after nearly two decades of legal wrangling, the U.S. Supreme Court lowered this fine to about $500 million after multiple appeals from Exxon. All told, the company says in a statement about the notorious anniversary that it has paid "over $3.8 billion as a result of the accident, including compensatory payments, cleanup payments, settlements and fines," and that "the 1989 Valdez accident was one of the lowest points in ExxonMobil's 125 year history."

Tragically, much of the damage might have been avoided with adequate emergency measures in place, says Rebecca Talbot, a spokesperson for the EVOSTC. A silver lining in the accident's aftermath has been a "leap in knowledge," says Talbot, gained from intensive monitoring of the short- and long-term effects of oil spills. The spill also had a galvanizing effect on lawmakers who passed the federal 1990 Oil Pollution Act to help stave off a repeat of the disaster by increasing oversight, stiffening penalties, mandating contingency planning, and creating new research programs.

Since the 1989 crash, the international push for double-hulling oil tankers—already well under way when the single-hulled Exxon Valdez spilled its toxic cargo—has increased, with the United Nations mandating a worldwide phase-out of most single-hulled ships next year. Tanker tracking and warning systems, aided by the advent of the satellite-based global positioning system (GPS), have improved tremendously, as well, experts say.

The key improvement since the Exxon Valdez incident has not been in hardware but in "peopleware," says Robert Bea, a professor of civil engineering at the University of California, Berkeley, (who has driven an oil tanker as part of his research). "What the incident did was began coalescing the international marine community to clean up its act and focus on people and not just [sea] vessels and the like," Bea says.

After all, human error played the biggest role in the accident, according to the National Transportation Safety Board's analysis, along with other official reports. Instructions from the ship's captain, Joe Hazelwood, to return the vessel to the shipping lanes after steering clear of icebergs apparently never reached the helmsman, Robert Kagan, at the time of the wreck. Anecdotal reports about seeing the captain at a bar prior to leaving port, confirmed by a blood test revealing alcohol in his body hours after the accident, also spoke to the lack of staff oversight at the time by Exxon and other oil companies with supertankers on the high seas.

But thicker and doubled hulls, better monitoring and a rested, well-trained crew will not always be enough, says Bea. When spills from tankers do happen, an array of cleanup and remediation techniques, along with specialized technology come to the fore, both to tackle the mess and save the wildlife caught in the wrong place at the wrong time. See the slide show to learn more about the consequences of the Exxon Valdez incident, and how both preventing and remediating oil spills' long-lasting effects have advanced in the last 20 years.

Slide Show: Preventing Another Exxon Valdez Disaster