RUSSELLVILLE ? Bob Allen cranked the ignition and climbed out to admire the exhaust note, a heavy chug stoked by a blend of frying oils and chicken fat from a local poultry plant.
   On other days, Allen has powered his metallic-gray 1981 Mercedes with grease from Brown?s Catfish and C-J?s Burgers. The 59-year-old Arkansas Tech chemistry professor gave up on the cooking oil from the campus cafeteria as too lumpy, but has collected four sticky cartons full of drippings from colleagues and students who deep-fried their Thanksgiving turkeys.
   He runs it all through a homemade chemical reactor, fashioned from a water heater, that converts waste grease into biodiesel ? a diesel fuel alternative made from animal fats or vegetable oils. He calculates the cost at less than $1 a gallon.
   While President Bush vows to break America?s ?addiction? to foreign oil and factories gear up to process alternative fuels from soybeans and chicken fat, a few individualists are already rolling into the future ? in old diesels powered by straight vegetable oil or by home brews from backyard reactors.
   With crude oil about $60 a barrel on the New York Mercantile Exchange, 53 U.S. plants have begun producing biodiesel on a commercial scale. Eastman Chemical Co. near Batesville turned out its first soy-based biodiesel in October and has already doubled capacity to 6 million gallons a year. Next month, Patriot BioFuels in Stuttgart will start converting soy oil and poultry fat into biodiesel at an annual rate of about 3 million gallons.
   The Arkansas plants contribute to a national output that tripled from 25 million gallons in 2004 to 75 million in 2005, according to the National Biodiesel Board, an industry group in Jefferson City, Mo.
   But so far, commercial-scale biodiesel is bound primarily for fleets and farms. The average motorist is unlikely to find any: Only 14 stations in the state sell biodiesel for on-road use, all in the eastern agricultural counties, according to the Farm Bureau.
   Pumps are more common in the Midwest, however, and as they spread, they will offer more motorists an alternative that promises less reliance on foreign oil at a price that is competitive largely because of hefty federal tax credits for blenders. Stuttgart One Stop was selling biodiesel for on-road use for $2.49 Friday, about the going rate for petroleum-based diesel.
   The stations sell blends that mix diesel with up to 20 percent biodiesel. Often, it?s only 2 percent ? a pale imitation for the purists.
   

IT MAKES SCENTS
   
No one knows how many Arkansans are making 100-percent biofuels in reactors like the one in Allen?s chemistry lab, or simply burning straight grease.
   The difference between the grease and the processed fuel is this: The reactor strips out glycerin, a syrupy compound in the grease. Removing the glycerin makes the oil thinner; cars running on straight vegetable oil need minor modifications to heat the grease so it won?t gunk up.
   Allen, who built the reactor to teach his chemistry students, offered a public workshop last fall and is planning another to satisfy growing interest. Lately, it seems that someone calls or drops by his lab nearly every week wanting to know how to get into the game.
   On Wednesday, it was a pair of business partners who drove in from Clarksville to explore processing their own fuel for their trucks, Allen said. A former student has assembled a couple of reactors for paying clients, and has sold instruction booklets on eBay for $15 or $20.
   But the professor guesses there are still no more than two dozen reactors cracking grease molecules in Arkansas.
   Those who prefer their vegetable oil straight have their own counts.
   ?I?ve sniffed out at least five vegetable burners, or substantial vegetable burners, that I haven?t even met,? said a straight-oil enthusiast who gave his full name as ?Sheba.?
   To a discerning nose, he explained, the exhaust is the tipoff. ?That one might smell like french fries, that one smells like vegetable tempura, that one smells like barbecue ? it?s really that distinct,? Sheba said as he admired the straight-vegetableoil Mercedes that was the focus of a recent vegetable-burner seminar in Little Rock.
   

?A LITTLE BIT OF PLUMBING?
Promoted on Little Rock Metro Freecycle, an Internet message board, the gathering was intended to promote alternative fuels and explore the possibility of organizing a biofuels resource center, according to organizer Jeff Dempsey, who said his interest stems from an appreciation for ?sustainable? lifestyles.
   In a parking lot outside a Little Rock recording studio, a crowd of 10 gathered around a dark-blue 1984 model with its hood propped open and its engine bathed in klieg lights.
   The midnight-blue sedan was equipped with a two-tank system so it can be started on diesel and then switched to vegetable oil once it?s warm. Owner Jebb Ingram, 18, pointed to a toggle switch near the steering wheel. He said other modifications included insulated copper lines to help keep the grease warm.
   ?A little bit of plumbing is all it is,? he said.
   He walked across the parking lot to a nearby Arby?s and flipped open the grease bin. Inside was a thick pool of perhaps 400 gallons of waste cooking oil. Ingram, who totes a filter and a pump, gets all he wants free from restaurants eager to get rid of the grease.
   ?I like Asian food the best,? he said. ?It seems to be the best quality. They tend to use the better-quality oils, peanut oils.?
   Ingram and Allen report no car troubles since going to alternative fuels. Allen said he?s driven perhaps 15,000 miles on his home-brewed fuels, and Ingram has clocked roughly 5,000 miles on straight restaurant grease.
   

ON THE OTHER HAND
   
But unlike commercial biodiesel, the homemade fuel is not held to ASTM International specifications drafted to protect engines, said Jenna Higgins, spokesman for the National Biodiesel Board.
   ?Straight vegetable oil is, first of all, not a road-legal fuel,? she said, ?and it is likely to cause engine damage.? She said the same concern applies to fuels from home reactors.
   Either fuel would void engine warranties, she added.
   The Engine Manufacturers Association says that, while there is limited information on the effect of pure biodiesel and blends on engine durability, it has confidence in ASTM-certified blends up to 5 percent.
   But adherents of grease dismiss such warnings as so much politics getting in the way of progress.
   At the seminar in the Little Rock parking lot, Robert Ludwig of Conway said his wife saved $90 to $150 a month on her commute to Little Rock driving a veggie-burner.
   In Stuttgart, Harvey Edwards is promoting his own biodiesel cooperative while he finishes converting his ?79 Mercedes to vegetable oil. His Arkansas Bio-Fuels Cooperative Web site offers plans to build a ?B100-WH Biodiesel Reactor? much like the one in Allen?s chemistry lab.
   Allen said he built his for about $150. It runs on lye, methanol and the grease, turning it into fuel in a process that Allen likened to making soap. But the reactor ? a confabulation that includes the water heater, a 55-gallon drum and a stainless steel vat connected by hoses and valves ? could be taken for an old-fashioned alcohol still, the professor had to agree.
   And here?s a familiar complication : revenue agents. Homefuel proponents say they don?t have to pay state and federal motor-fuel taxes that add 47 cents to every gallon of highway diesel, because their fuels do not qualify as legal motor fuels. But Higgins at the National Biodiesel Board begs to differ. ?People who make their own fuel are still liable for road taxes,? she said. ?So that would involve writing a check to the government.?
   Tom Atchley, state excise-tax administrator, tended to agree. ?If they?re creating a fuel out of it for highway use,? he said, ?taxes would be due.?