Does anyone use more (or only) premium than regular gasoline? Do you notice better performance or gas mileage? I drive mostly highway (65% or more).

From what I recall, people either see no change or a decrease in mileage, when they switch to a higher octane gas.

There is slightly more energy content in regular gasoline, and the Prius is not designed (from what I've read) to take advantage of higher octane fuels, so generally it's best to stick with regular.

Most cars will get improved torque so you can get up hills a little easier or dart off the line a bit faster, but the Prius provides most of that torque from the large electric motor that is unaffected by the octane of the fuel.

2001 Prius Photos       2005 Prius Photos
'97 Prius Simulation Prius inner workings

I would use what is recommended. The engines are already tuned and set up for economy rather than performance. High octane is not needed for computer controled cars except in cases where maximum performance (max hp) is required.

Aside from the higher price, in theory it wont be any use to your engine because it's not designed to take advantage of the higher octane . Most likely you'll get the same performance as regular, but dont quote me on that . My BMW's manual says minimum 91 octane, but i notice a significant increase in torque and better mileage if i fill with 94, but the difference is not worth celebrating about. The best way to fulfill your curiousity is to try filling up with it and see if you notice the difference, as long as you go above the recommended octane and not below it, your knock sensors shouldnt kick in .


good luck

I guessing you will get worse gas milage with the higher octane gas... prove me wrong.

I tried it more than once and got no difference in fuel economy. go with the cheaper gas.

***Follow Up:***

I filled up this last tank with Premium. I drive almost exactly the same route and amout every week. I found that I LOST nearly 2 miles mpg. I went from an average of 52.3 mpg the last 3 weeks to 50.1 this last time. The driving conditions were the same and were similar highway and city as with the regular gas.

I'll be sticking with regular.

As someone previously noted, when a car's engine fuel management system is designed to run on regular, premium will not help. The computer will actually retard the spark to cancel out the faster combustion of the higher octane fuel.

Good experiment although a couple of tanks would ordinarily be needed to equalize all variabilities. But it is helpful to review the Atkinson cycle used in our Prius engine.

The Atkinson cycle keeps the intake valve open during part of the compression cycle. This reduces the 'charge' and the compression ratio to 8-to-1. Reducing the compression saves the energy needed to compress the fuel-air mixture as well as reducing the fuel octane requirement. After the fuel-air mixture burns, the hot gases have a 13-to-1 expansion ratio. This provides the power stroke energy.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
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