I'm going to side with the guys that are getting less fuel mileage. When I was going to college(15-20 years ago). I was driving around 90 miles a day. I had a 4 cylinder Ford Tempo, and I routinely checked my mileage. On straight 87 octane, I would average around 25mpg and on 89 octane e10, about 23mpg. On the other hand, I'm comparing a regular unleaded to a mid grade. My car, and most of them out there are built to run on 87 octane. It only makes sense that the 87 is going to be more efficient than the 89. If I were comparing 89 e10 to 89 ethanol free, I believe the numbers would be more consistantly the same.
