At present, it goes into a pit at the landfill.

"Imagine a swimming pool full of grease with turkey vultures nine deep," said Navy Cmdr. Jeff Johnston, public works officer for the base. "It's not hazardous but it's disgusting."

To reduce the load on the landfill, the Navy recently bought a biodiesel processor to clean the used cooking oil and mix it with diesel fuel that powers much of the base.

Workers began testing technology on Friday to make their first batch of fuel, starting with used oil from the McDonald's restaurant. If all goes well, they will start testing the fuel on utility trucks and all-terrain vehicles by January and fuel local buses with biodiesel by June, said Fred Burns, energy and utilities manager for the base.

"When a bus goes down the street, you'll smell that french fry odor," Burns said.

Utility managers are unsure how strong the aroma might be but since deep-frying fish is popular on the base, faint might be better.

Base residents have already been asked to start putting their used cooking oil out in recycling bins with their cans and bottles.

The technology to make biodiesel has existed for decades but until recent years, gasoline was cheap enough that few people bothered with it, Burns said.

The Guantanamo base has more incentive than most communities to recycle locally as much as possible.

Landfill space is tightly limited on the base, which is rented from Cuba and completely isolated from the rest of the island because of frosty relations between the US and Cuban governments.

US law prohibits trade with communist-run Cuba and the Navy spends a lot of money to send much of its refuse by barge to Florida, hundreds of miles away, for disposal or recycling.

Guantanamo also has to bring in fuel by barge. The base relies on diesel to power its buildings as well as its vehicles, and burns through a gallon every 3 seconds -- US$65,000 worth each day, Johnston said.

"Every gallon of cooking oil we put in the tank is another gallon of diesel oil we don't have to buy and ship down," he said.