Have to disagree here. I use mostly 87 and get the standard 40-42. We have a place here that still sells "91 ethanol free", when I use that I get 43-45 mpg. I believe it also runs a little smoother on take offs. During this years rally, when we were in CO, we were getting 50 on some runs, but drop some elevation and get into Kansas, the mpg's dropped into the 30's