WASHINGTON — Gabe Schwartzman, a tall, lanky high school senior, can fill up the tank of his 1980 Volvo sedan for less than $20.

And he's happy to share his secret: "I take what would be thrown away and turn it into fuel."

Over the past several months, Gabe has been hunkered down in the basement of his parents' suburban Maryland home, converting used fryer oil from a restaurant up the street into fuel for his car.

Brewing biodiesel, once a quaint hobby for green-minded citizens and budding chemists, is becoming more mainstream. The spike in gas prices is making fryer oil, the messy aftermath of super spuds and mozzarella sticks, a hot commodity.

"It's the cool fuel," said Montgomery County, Md., Councilman George Leventhal, D-At Large, a biodiesel enthusiast. "Just think: You can turn bacon grease into fuel to drive a tractor."

Biodiesel is an alternative fuel made from combining vegetable oils or animal fats with other substances, most commonly lye and methanol. It can be used on its own or mixed with normal diesel fuel to power any vehicle that runs on diesel. Although the fuel is nontoxic, the chemicals used to produce it can cause nerve damage and even blindness if handled improperly.

Environmentalists like biodiesel because it burns cleaner and because some versions recycle what is essentially a waste product. A study conducted by the Department of Energy and the Department of Agriculture found that using biodiesel in place of diesel reduces carbon dioxide emissions by 78 percent.

According to Joe Jobe, chief executive of the National Biodiesel Board, about 500,000 gallons of biodiesel were sold in 1999 by commercial producers nationwide; in 2006, 500 million gallons were sold. But it is still a tiny part of the fuel market. In 2007, U.S. consumers used more than 142 billion gallons of gasoline.

There are no official statistics on the number of home brewers. About two years ago, Graydon Blair, a home brewer who sells biodiesel brewing supplies online, did his own survey and estimated there were about 20,000. With the spike in diesel prices in March, he expects that number to grow.

Before, his customers were "hippies and greenies," said Blair, president of Utah Biodiesel Supply. Now they're "desperate business owners — mom-and-pop operations who are dying with all these fuel increases."

Lately, Dan Goodman, a senior fellow for renewable energy at the University of Maryland's Robert H. Smith School of Business, has fielded calls daily from people seeking information on making biodiesel. Goodman is head of Biodiesel University, a mobile education lab aimed at getting students interested in science.

Goodman cautioned that making biodiesel can be time-consuming and tricky. He said it's critical for home brewers to do their homework and take safety precautions.

Gabe, who said he spends 50 cents to $1 to make a gallon of biodiesel, spent several months poring over "From the Fryer to the Fuel Tank," a book some call the brewer's bible, before attempting his first batch.

Finding used fryer oil, however, was trickier than he expected. Local restaurant owners weren't quite sure what to make of the lanky, long-haired teen when he showed up offering to cart away their used fryer oil for free.

"I got a lot of weird looks," Gabe said.

Eventually, he struck a deal with local restaurant Red Ginger, which specializes in Chinese food. Every couple of weeks, Gabe carts away up to a half-dozen 5-gallon containers of used oil.

In his basement "laboratory," Gabe, clad in a rubber apron, apologized for the sticky floor, explaining that while biodiesel is a clean-burning product, its processing is quite messy. Of the three main ingredients Gabe uses, lye burns the skin on contact, and methanol can cause nerve damage if absorbed through the skin, and blindness if it gets into the eyes. Gabe always wears goggles and keeps a fire extinguisher close by.

"It comes with all the glop — whether it's peanut sauce or chicken," Gabe said as he used what looked like a giant turkey baster and a pair of pantyhose to separate out chicken pieces and stray cashews. The next step was to make a test mixture. Because each batch of oil is different, depending on what it was used to fry and how long it was in service, the amounts of lye and methanol must be calculated each time.

Once that was done, it was time to brew. Gabe added a mixture of lye and methanol to the used oil. Then he attached a super-sized version of a hand blender, flicked it on and stood back. At the beginning, it looked like brown gravy. After about 15 minutes, it darkened to resemble chocolate sauce; after a few more minutes, it took on a reddish tint and smelled of chemicals.

Gabe poured it into a holding container, where it sat for several hours. Eventually, the biodiesel rises to the top, and glycerol sinks to the bottom. The glycerol is drained, and the biodiesel is rinsed with water. When ready, what was once gloppy brown oil is a clear, amber-colored liquid.

The real test comes each time Gabe fills his tank. Even though he has completed several batches, he still admits being a little nervous when filling his fuel tank.

"The first time I tried it, I messed up terribly and ended up with a giant vat of soap," Gabe confessed, noting that glycerin, the main ingredient in soap, is a byproduct of the brewing process. "Really, really greasy soap."

He pried open the tank cover and poured the home brew into the car.

He climbed into the driver's seat and turned the key. The car slowly rumbled to a start and promptly spit out a sizable cloud of exhaust. He hit the clutch, shifted into first, and his green Volvo chugged away, leaving the unmistakable scent of fried egg rolls in its wake.

Gabe Schwartzman, a high school senior, strains used soybean oil to make biodiesel fuel at his parents' home in Garrett Park, Md.