I use ethanol free gasoline in our Prius year round just because I like the bump in mileage I get, and I do not like ethanol in general. Granted I suppose any little bit of energy independence we can get is crucial I feel that it does nothing but actually increase our oil consumption by lowering mileage. Not to mention in E85 vehicles the decreased maintenance intervals for oil changes. Unfortunately though where we move in Virginia has absolutely no ethanol free gas available, so this will probably be the last tank to go into our Prius for awhile sadly. Hopefully they don't implement the E15 standards.