For at least a couple of years, diesel has been generally more expensive than gasoline--infuriating since it's a byproduct of making gas (can you tell me why?). And unless you're in the midwest, biodiesel is usually pricier than petroleum-based diesel; blame shipping costs. But if you're thinking about trying biofuel, now might be the time to feed it to your old Benz or new Jetta. With old-school diesel in the Bay Area costing between $3.12 and $3.69 per gallon, biodiesel is finally looking cheap--or at least comparable--by comparison. Bay Area Biofuel has knocked its cost down to $3.25/gallon. Alas, it's $3.65 at the Biofuel Oasis and between $3.50 and $3.90 at the SF Biofuels Cooperative. Check out other U.S. biodiesel fueling stations on this map.