I always used to use 93 octane since I couldn't find just 91 octane. Since a retired VP of Standard oil told us to just go for the mid range 89, that the didfference is more marketing than any appreciable difference, that the premium is just a waste of money and he puts the midrange octane in his top of the line Mercedes; I decided that is what I'd do. I had thought of the idea of mixing rpemium and 89 oct. but never seem to think of it at the time or want to take the extra time to do so.