The biodiesel band bus.

Zachary Matthews, who sings and plays mandolin and fiddle with the Hot Buttered Rum String Band, fondly recalls how he and his band mates met ... on a backpacking trip. The call of the wild brought them together, and it keeps them together. The environmentally conscious band tries to leave an impact on its fans, and not solely on the road that passes beneath its bus tires as it travels from coast to coast.

While researching alternative fuels, the band heard about the biodiesel option from the Ecology Center in Berkeley, California. The group attended workshops and learned how to run its diesel bus on vegetable oil; the "Bio Bus" hit the road in the summer of 2003 and has since logged more than 50,000 miles.

Veggie buses are cool these days. Top players with biodiesel bus conversions include Neil Young, Dave Matthews and Jack Johnson. "One of my pet projects is to run the next Greendale tour on biodiesel," said Young in Wired last year. "It gives off 80 percent less emissions. If we travel with a giant thermos-bottle truck with 'biofuel' written on the side, the TV people will come, and then I'll be able to prostitute myself for something positive, instead of just selling a record."

Dedicated "grease" user and singer-songwriter Jaia Suri converted her Ford 350 to pure biodiesel and personally thanks restaurant owners on the road for allowing access to their used fryer oil.

With both gas prices and global warming concerns on the rise, interest in renewable fuels like biodiesel--which in one common form is 20 percent vegetable oil, 80 percent petroleum diesel fuel--is increasing. According to the National Biodiesel Board, the blends can be used in any existing diesel engine with very little impact on the vehicle's operating performance.

To run B100 vegetable oil, diesel vehicles need a $1,000 kit available from several manufacturers. Biodiesel fuel eliminates carcinogenic sulfur emissions and reduces most major exhaust pollutants, particulate matter and the greenhouse gas carbon dioxide. Biodiesel even smells better than gasoline: many say they catch a whiff of French fries.

Zac Matthews says the group bought its first biodiesel vehicle on eBay in 2003. "This school bus was the famous Project BioBus converted to run on veggie oil by 13 students of Middlebury College in Vermont" he says, adding that the group parks the bus in front of the evening's venue and after the show offers demonstrations on how the bus works. Matthews feels it's important to encourage others to convert their own vehicles.

One of the most enthusiastic supporters of biodiesel is singer Willie Nelson, who helped found The Willie Nelson Biodiesel Company partnership last year. The company's fuel, "BioWillie," is mostly made from soybeans and can be burned without modification in any diesel engine. Nelson says the furl reduces the need for imported oil and helps one of his favorite causes--American farmers--at the same time. CONTACT: National Biodiesel Board, [phone], www.biodiesel.org; Hot Buttered Rum, [phone], www.hotbutteredrum. net; Willie Nelson Biodiesel, [phone], www.wnbiodiesel.com.