I filled up my car a few weeks ago with Valero 93 Octane premium fuel. I got around 415 miles of driving before I had to fill her up. I then filled up with crappy Murphy (walmart) 87 octane gas. I drove the same routes I did when I had the premium fuel but this time only got to about 375 before having to fill up. Anyone else notice this big of a difference in fuel mileage on reg gas vs premium? My cars a 97 se with 138k on it by the way.

 

There are WAY too many variables to accurately say that octane makes a difference. There is just no way you can drive 'the same routes' using the same amount of throttle, and account for the same amount of idling at red lights. It's just not possible. BUT, in general, the higher octane gas should get you a little better gas mileage.

 

There have been numerous threads about this. Search.


IBTL.

 

You might as well start a political debate! You'll get all different kinds of "educated" opinions around here.

I get about 29-30 MPG mixed driving with a 3.5 and AT. I ONLY use Premium because the 87 gives my car much lower MPG, as observed by me. being that Premium is only $0.20 more per gallon, I also save money burning Premium.
However, on my old 3.0 motor it could run 87 or 91 and get the same MPGs, so I used 87 before. If you observe better MPGs on 91, I'd use it. YMMV

 

Don't be cheap. Use 91+.

 

It's not just the octane. The different brands can have different blends. The density can be different. Heavier gas will give you more MPG. I would suspect that if you get good MPG with one brand @ 91+ octane you might get as good with the same brand @ 87 octane. This asumes that you are not putting a high load on the engine.

 

This may sound crazy but this is what I have noticed. It makes a difference how your car is positioned when you fill up the tank. If your on a slight downward slop you can get up to 2 more gallons in the tank, thus increasing your distance on that tank of gas. When checking your mileage you should fill up at the same station and pump with your car facing in the same direction. I guess you want to eliminate as many variables as possible. Then try different octane ratings from that same pump..
Just my 2 cents worth..

 

lower octane makes me mad. When i can't accelerate properly (automatic) i lean on the throttle a little more. (subcontiously) So it makes sense that more hp translates into a smoother acceleration track. In my experience, that means better gas mileage on premium vs. regular.