Environmentalists with diesel cars have used vegetable oil for years as an alternative fuel to cut back on sooty emissions, but as gas prices climb above $2 a gallon, they say their "veggie cars" are a great way to save cash.

Every two weeks, Etta Kantor drives to a Chinese restaurant to fuel her Volkswagen Jetta. She calls ahead and the owner puts aside a few buckets of used oil for her. At home, Kantor uses a colander and a bag filter to remove water and any food particles.

The vegetable oil is then poured into a 15-gallon tank in the back of her Jetta, where a spare tire would usually be kept. With a touch of a button above the radio, Kantor can switch from diesel fuel to vegetable oil in seconds.

"Oh, I zip around town, go fast on highways. It's not any different," said Kantor, 58, of Weston.

Restaurants that would have to pay to get rid of their old vegetable oil are happy to give it away for free.

"It saves us a couple of dollars and it helps to save the environment a bit so I thought, 'Why not?' " said Shawn Reilly, a co-owner of Eli's On Whitney, a restaurant in Hamden, Conn.

Reilly estimates it costs as much as $60 a month to have the oil removed otherwise.

Bridgeport resident Aaron Schlechter says he picks up about 30 or 40 gallons twice a month from Eli's. He uses it to fuel his car for his 170-mile commute every day to his job as an environmental consultant in Staten Island, N.Y.

"The only way that I can assuage my guilt by driving this awful distance is by driving something that isn't consuming fossil fuels and has much more environmentally friendly emissions," Schlechter said.

Vegetable oil is becoming so popular that a Massachusetts company called Greasecar is buying it in bulk from a distributor and selling it to local customers. It's priced at 90 cents a gallon, said company founder Justin Carven.

Since 2001, Greasecar has also been selling conversion kits, like the one in Kantor's car, that allow diesel cars to run on the recycled oil. About 200 kits were sold in the past year, Carven said. A standard conversion kit sells for $800 at Greasecar.

"Once you install it, though, you are saving hundreds and hundreds of dollars," Carven said. "The product usually pays for itself within the first year."

Cars that have a conversion kit have two fuel systems, one that operates on diesel and the other on the recycled oil. The car is stopped and started with diesel; once it's running, the vegetable oil is heated to make it thinner. The driver can then switch fuel systems and the recycled oil is sprayed into the engine in the same way diesel fuel is.

The kit works only on diesel engines because vegetable oil is not flammable enough to work in gasoline engines that are spark-ignited.

Liquid Solar in Ithaca, N.Y., has contracts with a few local restaurants to collect their used vegetable oil. And in Santa Rosa, Calif., a group of 50 people have formed a co-op to buy oil in bulk from a local manufacturer and then filter it for their own use.

Although the Environmental Protection Agency has approved vegetable-based biodiesel, which also is gaining in popularity, it hasn't OK'd any recycled oil for sale, said Christine Sansevero, an environmental engineer for the federal agency.

"You just don't know what's in that oil," she said. "There could be metals, other chemicals that, when burned, could create something you didn't intend to burn. It could also be fine, but it's an unknown."

Biodiesel is a fuel derived from plant oil or animal fat, Sansevero said. It can be used in pure form but it is often blended with regular diesel. The most common form is B20 — a blend of 20 percent biodiesel and 80 percent petroleum diesel.

Veggie car owners agree that biodiesel is another renewable fuel source, but say it isn't as cost-effective or eco-friendly. Pure biodiesel costs about $1 more per gallon than diesel, Sansevero said. B20 costs about 20 cents more per gallon than diesel, she said.

The trend is catching on, especially for those who have quite a distance to drive.

The Healing Waters Band had a Greasecar conversion kit installed in its bus for a recent seven-week tour across the country. The band used a blended biodiesel mix to start and stop the engine, and vegetable oil for the rest.

The band left its hometown of San Diego on a full tank of vegetable oil and then filled up again at a Chinese restaurant in Missouri before buying 500 gallons during a stop at Greasecar in Massachusetts.