Heat is integral for the SVO mechanical process. Hartlieb aims to heat the drums of waste vegetable oil 150-160 degrees. The drum is lined with a filter that collects food particles. During the heating process, the oil rises over the water, and Hartlieb can drain the water from the bottom of the drum. Remaining in the tank is a thick, coffee-colored substance that's the SVO fuel.

"Imagine salad dressing: vegetable oil and water," Hartlieb says. "In the fridge, it's mixed and gets thicker. If you take it and raise the temperature, it quickly wants to separate. Or hot water and washing dishes, it cuts the grease."

Usage by the numbers

As a result of the differences between the two biofuels, fewer drivers use SVO fuel than biodiesel. But it's hard to determine just how many people use fuels derived from vegetable oil, because so much of it is made in private garages.

In 2007, 500 million gallons of biodiesel were produced in the United States for retail, says Amber Thurlo Pearson, spokeswoman for the National Biodiesel Board, which represents the industry. In comparison, the U.S. Energy Information Administration estimates that in 2007, the United States consumed more than 142 billion gallons of gasoline.

Biodiesel can be sold in blends with petroleum diesel. It's obvious at the pump: B20 indicates the blend contains 20 percent biodiesel and 80 percent petrodiesel. B100 is 100 percent biodiesel.

Perhaps the most famous biodiesel brand is BioWillie, a B20 blend made by Earth Biofuels Inc. and endorsed by country music singer Willie Nelson. BioWillie is sold primarily at truck stops in California and six Southern states.

The National Biodiesel Board, based in Jefferson City, Mo., began in 1992, during the early stages of biodiesel development. The board touts the benefits of the fuel: It's made of plants grown by American farmers and could provide the country with a fuel source that's more immune to global politics. It's a renewable source of energy. Low blends of biodiesel cost the same as petroleum diesel. And biodiesel emissions are lower.

A 2002 EPA report compared soybean-oil in a B20 blend of biodiesel and 100 percent petrodiesel. With the B20, emissions from carbon dioxide decreased 11 percent, hydrocarbon decreased 21.1 percent, particulate matter decreased 10.1 percent and nitric oxide increased 2 percent.

About 1,400 retail sites throughout the United States sell biodiesel, including about 800 truck-accessible pumps. In Utah, about 20 stations sell biodiesel from Logan to Moab.

The biofuel underground

Graydon Blair of Syracuse sells supplies for making biodiesel at UtahBiodieselSupply.com. He started the business in 2005, a side venture while working full time for Intermountain Healthcare. He likened his business to "selling supplies to make beer, but I sell the supplies to make biodiesel."