Tamar More, a conservation-minded physics professor in Oregon, gets almost 21km to the litre in her diesel Volkswagen Jetta, whose tailpipe fumes smell like french fries.

More runs her car on biodiesel, a fuel derived from vegetable oil or animal fat, not petroleum.

Most United States biodiesel comes from Midwestern soybeans, but Oregonians are tapping spent oil from restaurant deep fryers.

With crude oil selling between US$55 and US$60 a barrel compared with US$36 a year ago, the use of vegetable oil as car fuel is winning converts.

Brian Jamison, co-founder of a Portland co-operative that produces the fuel, says biodiesel is a way for people to become less dependent on oil companies.

"It's easier to make biodiesel than it is to make cookies from scratch," says Jamison, 38, who runs a software company called OpenSourcery when he's not cooking up fuel.

The co-operative collects used oil, adds methanol and a small amount of potassium hydroxide, and turns it into biodiesel and glycerine, the raw material of soap.

The co-op aims to produce enough to supply its 80 members when it starts full production this year.

More, 39, says she is proud to use biodiesel. The fuel produces less carbon monoxide and fewer particulates than petroleum-based diesel and eases US reliance on foreign oil.

"I wanted a station wagon but I refused to have a car that got less than 40 miles to the gallon," says More, who teaches at the University of Portland.

She was so sure about her choice that she bought the car without a test drive.

Like many users, More has a blue-and-yellow "Powered by Biodiesel" bumper sticker on her car.

In Portland, which has one of the highest recycling rates in the US, the interest in biodiesel has caused people to covet diesel Volkswagens.

"I constantly have people asking me about it," says More.

The vehicles are hard to get. Volkswagen is one of only two car-makers selling diesel passenger cars in the US.

DaimlerChrysler has the Mercedes E320 sedan, which retails for about US$51,000, compared with US$20,000 for the Jetta wagon.

"We're selling them as fast as we get them," says Duane Fulps, fleet manager at a Volkswagen dealer in a Portland suburb.

Volkswagen spokeswoman Marijke Smith said drivers did not have to modify their diesel engines to run on biodiesel, but the fuel was acidic and tended to destroy any rubber parts in engines.

Unlike diesel cars, the fuel is becoming easier to find in Oregon. SeQuential Biofuels co-founder Tomas Endicott, 33, has been shipping it in on railcars from the Midwest for three years.

Endicott's company and Pacific Biodiesel of Hawaii are building a plant in Portland to make as much as 15 million litres of biodiesel a year.

Among their investors is country singer Willie Nelson, who started Willie Nelson Biodiesel in Dallas in January.

Feed for the plant will come from Kettle Foods, maker of Kettle brand potato chips, in Salem, Oregon.

Kettle uses safflower oil to cook its chips and is committed to sending SeQuential 30,000 gallons of used oil a year.

Kettle Foods is a biodiesel user already. It has three company cars - all Volkswagen Beetles - running on it.

The idea of running cars on vegetable oil is as old as the diesel engine itself.

German inventor Rudolph Diesel, who patented his namesake engine in the 1890s, built some that ran on peanut oil.

Now, with oil predicted to go even higher than US$60 a barrel, the idea of running cars on vegetable oil is gaining popularity.

Jamison constructed his biodiesel refinery on the cheap to prove that it can be done. It's housed in a steel shipping container that he bought for US$1400 and planted on a site on the outskirts of Portland.

He uses a beer keg, modified with hoses and spigots, to combine potassium hydroxide and methanol. That mixture flows into two 208-litre drums holding the oil that co-op members bring from restaurants.

Jamison heats them to 140 degrees and then lets each batch settle. The biodiesel comes out on top and glycerine on the bottom. He makes soap with the glycerine.

The co-op plans to charge members US$2.25 a gallon for the fuel. Regular diesel sells for about US$2.40.

Jamison estimates that each gallon of biodiesel costs about a US dollar to make. Federal and state excise taxes add 49USc.

Veggie power

* The idea of running cars on vegetable oil is as old as the diesel engine.

* German inventor Rudolph Diesel, who patented his namesake engine in the 1890s, built some that ran on peanut oil.