My mileage went from 39 to 45? 2007 prius

[spitinuri]

Ethanol content or the lack thereof is the culprit. In Missouri the law states that all grades must have 10% Ethanol. The only exception is for boat fuel (seem they found that Ethanol damages boat motors). I'm averaging 48-52 mpg now that it is getting cooler. I would love to have the extra 5 mpg.

[The_Gunrunner]

Originally Posted by JacksonMs

I have a 2007 prius touring... I drive about 100 miles highway round trip to work daily...
generally, my MPG is around 39 highway. The other day, I accidently filled up with premium unleaded instead of regular... My MPG increased to 45 with no change in the way I drive...
Has anyone else noticed a change in MPG based on what grade fuel they use?

Thanks!

Gadget Dad is right. A lot of things that can influence the way your Prius uses fuel. It's fall right now so more than likely you're not using the air conditioner or heater very much, if at all. Second, octane is a chemical compound added to fuel to regulate the rate of burn. Only higher compression engines in sports cars require premium fuel. It won't hurt your Prius, but it certainly won't help. You just wasting money with premium. However, it does help out a lot to use Plus-rated fuel (usually 89-90 octane) when you're using the air conditioner. It will reduce engine "knocking" (pre-ignition) during the summer months.