WASHINGTON, Dec. 22  A federal appeals panel on Friday cut nearly in half the $4.5 billion punitive damages award against Exxon Mobil as a result of the Exxon Valdez oil spill in 1989.

A majority of a three-judge panel said the company’s negligent conduct, while “particularly egregious,” had not been intentional and had not warranted the maximum financial penalty that a lower court imposed.

The panel of the United States Court of Appeals for the Ninth Circuit, in San Francisco, split on applying legal precedents to the company responsible for the worst oil spill in United States history. It cut the award for punitive damages to $2.5 billion.

In the decision, the majority wrote, “Exxon’s reckless misconduct in placing a known relapsed alcoholic in command of a supertanker, loaded with millions of barrels of oil, to navigate the pristine and resource abundant waters of Prince William Sound, was reckless and warrants severe sanctions.”