Now VW has come out with this years TDI Diesel and it's ultra clean burning even with low sulfur instead of bio that no matter what you put in the tank, you're contributing way less harmful emmissions. The factory website touts 97% less sulfur and 95% less sotty emmissions
A buddy of mine sent me these link for a promotional stunt that a local dealer here in Seattle did. Called Auburn to San Francisco on a tank of fuel it's a series of video shot "from the road".
Check it out, it' fun, and definately worth a look. Beyond the obvious, it really does show that we're "evolving". And nice to know that being green comes with options!