Fuel mileage with ethanol v/s non ethanol gas in my Civic was tested over a long period of time with repeatable results. Only other difference in the gas that I am aware of was ethanol free was 90 octane and ethanol gas was 87. Maybe some emissions additive in the 87 had something to do with it? Stumbled on the mileage difference after I found a station near Gadsden AL that sold the ethanol free for the same price as other stations charged for the 87 swill. It was on my regular route I drove for work through that area twice per week for over a year.