Mendocino County authorities are investigating the theft of about $5,500 worth of gasoline from a gas station in coastal Gualala, where the culprits arrived by night, jimmied or hacked into the dispenser and pumped more than 1,100 gallons of Super unleaded fuel into a U-haul box truck.

The fuel's disappearance was discovered Wednesday when a morning clerk at the Chevron did a tank measure and found a difference of more than 1,100 gallons from a similar check conducted when the station closed at 8 p.m. the night before, clerk Cindy Broesamle said.

A review of surveillance video revealed the theft.

The footage showed a sporty black Trans Am-like car and a beat-up U-haul truck arriving at the station around 4:30 a.m., with the truck pulling up to the pump, Broesamle and the Mendocino County Sheriff's Office said.

Perhaps using a key typically employed by maintenance or inspection personnel, the thief was able to unlock the pump, punch in a code or otherwise manipulate the electronics and pump a large volume of fuel into a tank in the back of the truck, they said.

The license plate was covered, preventing identification of the vehicle, Broesamle said.

Super unleaded at the Chevron is currently priced at $4.60 a gallon, just raised from $4.55, she said.

Authorities put the estimated value of the stolen fuel at $5,500.

The manager of the Unocal 76 station across Highway 1 said he thinks someone tried and failed in a similar attempt there last week, though the would-be thief instead ended up shutting down the pump.

Unocal manager Bob Sundstrom said the pump wasn't working when the station opened one morning and the internal computer code indicated the pump had failed.

A maintenance tech said it had been tampered with, and it appeared someone used a key to unlock the pump and punched in a code but couldn't make it work.

Tank measurements and other records suggested no gas was missing, Sundstrom said.

Industry representatives likened the keys used for older dispensers by service technicians to the universal key a hotel maid might have that works in every room of an inn.

Abuse of the keys is not new but is more prevalent around California in recent weeks because of skyrocketing gas prices.

Greg Taylor, transportation manager for Redwood Coast Petroleum in Santa Rosa, said similar thefts had occurred in the Los Angles area and near Crescent City.

"I'm aware of the problem," said Jay McKeeman, a spokesman for the California Independent Oil Marketers Association. "It's been reported in a variety of trade publications that this is a continuing problem."

Anyone with information about the Gualala case is asked to call Mendocino County Sheriff's Deputy Mike Gander at (707) 463-4086, the sheriff's office said.