Interesting. Sorry to get too detailed.
E10 has 2% less energy than a standard gallon of petrol. Petrol is also mixed differently from summer to winter and the difference in energy per gallon is about 3% between them. If you want to get more miles per gallon fill up in the early morning and in cold weather. The fuel is denser so you get a very slightly more energy per gallon. Oh, and there is less ethanol in high octane fuel so more energy.
I still run my cars on higher octane fuel, and octane improver as well, for some!
