Performance hit
In the Spring and in the Fall there are times when I don't need to run the rear window defogger or the air conditioner in my car. If I drive mostly highway miles on a tank of gas then, I can get almost 40 mpg. Almost. Somehow I never quite seem to make it to 40 mpg. The last tank, however, did it. I got better than 42 mpg. While it was mostly highway miles, and at speeds of 55 and 65 mph, that's not likely the reason for the improvement. It was the gasoline.
No, really. It's not that it was a special brand, it was that I filled the tank in Wisconsin. Wisconsin, overall, uses straight gasoline. I had been filling the tank, naturally, in Minnesota. In Minnesota, almost all gasoline is 10% ethanol. It takes 1.4 gallons of ethanol do the work that 1 gallon of gasoline does. So by filling up in Wisconsin, I had more energy in the tank than I when I fill up in Minnesota.
Please note that I have not said that ethanol is bad idea. Or a good one. I'm just noting the difference in energy as it presented itself to me.