A crippled tugboat that spilled fuel into Alaska's Prince William Sound after hitting the same reef that caused the Exxon Valdez oil disaster 20 years ago reached port early Sunday morning, a spokesman for the tug's owner said.

The Pathfinder arrived under tow into Valdez, and crews will now work determine how much diesel fuel spilled into the bay after the tug ran aground on Wednesday, Crowley Maritime Services spokesman Jim Butler said.

Responders hope to have an answer late Sunday but it could take longer to examine all materials used in cleaning up the spill to make that calculation, Butler said.

The Coast Guard said that two of the tug's tanks — containing an estimated 33,500 gallons of diesel fuel — were damaged.

On two separate occasions, diesel fuel sheens of one mile and three miles spread across the waters. But officials said no animals were injured and the fuel didn't reach land.

The boat is part of a ship escort service created after the Exxon Valdez spilled nearly 11 million gallons of oil in 1989.