[ALS]

First off you run the octane that the owners manual says you're suppose to run in the car. If it says regular and you're running premium you're just wasting money.

Does better gasoline affect fuel mileage? From my experience yes in a big way.
Two cars, the first my fuel sucking pig a 1997 Volvo 960 with a 2.9L 24V engine. Manual says premium and over the last decade or more I've basically fed it what ever premium I could find that was cheapest.

A good friend does fuel mileage testing for some of the auto manufactures here in the states and he uses Shell gasoline exclusively. When I got this car it would get between 29.25 and 29.5 mpg (U.S.) on the highway at 65 mph.

I'd say since 2007 I've watched the highway fuel mileage drop slowly into the low to mid 26's. I had pretty much came to the conclusion it was the mandated E10 fuel that was causing the loss in fuel mileage.

So after a conversation with my buddy I ran the tank down to almost empty and tossed in a bottle Techron fuel system cleaner and filled up with Shell V-Power + Nitro. Took it out on a Sunday for a long ride to see if there would be any change. About 200 miles out there was a big change that caught me by surprise, the engine smoothed out to the point that it grabbed my attention immediately. It was that dramatic of a change.

I didn't see any change in the fuel mileage during that day or during that tank of fuel. I'd say it was the third tank of Shell V-Power when I saw the change in fuel mileage. I took the car out for a long drive to see a car museum and on my way up I noticed my Scan Gauge was pushing through 27 mpg (U.S) and went to the mid 29's and stayed there until I got to my destination. On the return trip it never fluctuated more than a few tenths one way of the other and I still ended up with 29.2 mpg (U.S.) for the 400 plus mile trip.

My other car a 2010 Prius is my daily driver and again I had use the cheapest regular gas I could find most of the time. I did the same routine a few months later, I tossed in a bottle of Techron to jump start the cleaning process and filled it with Shell regular gas. I ran a few tanks through it and didn't see much of a change in fuel mileage due to short trips and lots of hills around me.

I had a chance a few months ago to make a longer than usual highway trip in the car and was pleasantly surprised at my fuel mileage increase. Normally I would get 52-53 mpg (U.S.) on the highway at 65 mph. Now the cars fuel mileage had increased to 56 mpg (U.S.).

A few weeks ago I wanted to see if the mileage had stayed up or that earlier trip was a fluke. I ran the car all day on the highway at 55 mph (Cruise) with the AC running for over 300 miles and I ended up with a 61.3 mpg (U.S.) average (Scan Gauge) for the day.

For me personally I'm sold on Shell gasoline and if I can't get it I'll only use another TOP TIER fuel in either car. Fortunately the local Shell station by my home is the same or only two or three cents more per gallon than the off brand stations.

The benefits of the Shell over the off brand is it will clean the crud out of your fuel system over a few tanks of gas and keep it clean. If the Shell is prohibitively expensive you might want to run a fuel system cleaner through the car every couple months as a preventative measure.

There have to be other gasoline suppliers near you other than Shell, that have a higher than mandated detergent package in their fuels. Here in the states they are referred to as Top Tier fuels due to the much higher concentrations of engine cleaning detergents.