A tugboat operator says as much as 6,410 gallons of diesel fuel spilled in Alaska's Prince William Sound when a tugboat ran aground on the same reef as the Exxon Valdez 20 years ago.
Crowley Marine says the spill estimate from last month's grounding of the Pathfinder is considered a worst-case amount.
Crowley says the estimate is based on an evaluation of the tug's two damaged fuel tanks, the amount of diesel on board when it ran aground Dec. 23, and the amount recovered from the two tanks after it was towed to Valdez.
The estimate was reported Monday to oversight agencies including the Coast Guard and state Department of Environmental Conservation.
The 1989 Exxon Valdez disaster remains the United States' worst oil spill, with nearly 11 million gallons of crude oil spilled.