It is difficult if not impossible to find ethanol free gas in the St. Louis area. So while in Columbia, Mo. last week I filled up...Not for the higher Octane, but to see if the "pure gas" would make a difference. 91 Octane "pure" gas. (I like corn but not in my gas) Average 41.42mpg (real) 44.0 on the car meter. As I've only filled up twice previously, with real world mpgs at 42.6 and 43.2, it was no better. The ambient temp was a bit colder this week, so I believe the temp did have a bit of effect on the rating...
Thanks for reporting to us. St Louis is an EPA reformulated gasoline (RFG) region, which explains the lack of E0 (same here). Typically RFG is a little lower energy content, so you might see a little better MPG just getting outside of the immediate region. If your base case is RFG E10 (St Louis) then the E0 outside St Louis almost certainly has more energy content (min. +3%). What I do by the way is get exactly 1.5 gal sample in my lawn mower container and measure grams, whereas energy content relates to weight/vol density. But I don't do this too often since I live in RFG region, so not much variation, and when I am traveling, its a pain to carry my smelly gasoline can.
Been a long time, and not a very relevant study, but some years ago I did 5-tank samples in my Tacoma V-6 4x4. Compared premium, regular and regular with Ethanol. (15 tanks total). There was no difference between premium and regular, but the reg with Ethanol yielded roughly a 0.5 MPG decrease in MPG. I think I sampled enough tanks to rule out other factors.
E0 is very easy to come by where I live. So I tried several tanks of regular E0 in the Prius. I did not notice any real difference, certainly not enough to justify the about 15% increase in price over E10.
