Prince William Sound shows little sign of the 1989 accident that dumped 11 million gallons of oil into its turquoise waters. Fifteen years later, the sound boasts gleaming waters, immaculate beaches, and abundant wildlife. But researchers working for the government continue to square off against reseachers employed by Exxon regarding whether the spill has caused long-term damage. At the heart of the debate is an additional $100-million that the oil company would have to pay the government if research determined that there was continuing, unexpected damage from the spill.