Higher Octane for the better mileage.

Q: Why does it matter what kind of octane you use in your vehicle?

A: The octane rating on gasoline specifies its compression resilience.  Higher octane gas can withstand higher compression (such as high performance vehicles with super or turbo chargers).

Q: Did you know that you actually get stronger compression on higher mileage vehicles?.

 A: This is caused by the build-up of carbon deposits on your valves and pistons. If you are having mechanical problems with those higher mileage vehicles, make sure you are running a high octane gasoline before trying to figure out if there is anything else wrong. Carbon build-ups can also be worn down a little bit with the use of a product like SeaFoam Engine Treatment.  It is expensive, but it works well. Use it through the main brake booster line, and/or in the gas, and some people will put it in the crankcase shortly before an oil change.