A federal appeals court ruled yesterday that a $5 billion punitive damage award levied against ExxonMobil for the 1989 Exxon Valdez oil spill is excessive. The decision stunned environmentalists and the roughly 10,000 fishers, Alaska Natives, and others who have been awaiting compensation for more than a decade. When a jury handed down the verdict in 1994 for the 11 million-gallon spill in Prince William Sound, it was the largest punitive damage payment awarded in U.S. history. Yesterday, the 9th U.S. Circuit Court of Appeals said the award far exceeded the standard four-to-one ratio of damages paid to economic harm done to plaintiffs. Bringing the award into line with that ratio could decrease it to as little as $1.2 billion.