[Swordsmith]

I converted my Sonic over to run E85, in part for increased power (which certainly delivered) but also in part to reduce my petroleum use.

I average 33 mpg running gasoline with 10% ethanol and driving like I normally do, which is to say hard pulls up onramps, 15 miles over the speed limit, dropping down to fourth to pass people and generally misbehaving. Driving the same way on E85, I get about 22mpg.

Driving nicely, not hypermiling, but taking it slow, shifting early, keeping the rpm under 2K as much as possible, and staying within a couple mph of the speed limit, I get as high as 40 mpg on gasoline, and on my single test tank of this strategy for E85, 31mpg.

Doing some back of the envelope calculations, I seem to be getting
normal gasoline driving, 37 mpg of gasoline
sensible gasoline driving, 44 mpg of gasoline
normal E85 driving, 147 mpg of gasoline
sensible E85 driving, 207 mpg of gasoline

Now of course ethanol isn't completely harmless, and is often produced using petroleum, so this isn't a totally fair comparison, but on the face of it, it looks like running E85 is a very green mod, at least in terms of dramatically reducing petroleum consumption.