Newbie here. Getting my 05 Prius (pkg 6) this week hopefully. The only difference in the gasolines is in the additive packages which have stabilizers and detergents to keep the gas fresher longer, and to help keep the intake system and combustion chambers clean. In general, always buy your gas at a location that sells a lot of gas. This way it will be fresher and you should get the best mileage.

Rich