I run premium where the rating is 93 where I fill up. Since the cost difference is only $.10 more than regular where I get mine, I just don't see it necessary to go with the lower grade. I will say when I was out of state recently and came across a station that if I remember premium was only 89 or 90 and didn't have ethanol, my gas mileage improved about 3-4 mpg.

I've heard of people only running regular but every 4th fill up they would go with premium and never saw any ill effect, but that is a far cry from a structured test to determine any impact.

Now on that note, I find it interesting there appears to be a correlation between the requirement for better MPG of automakers, which impacts the oil industry, and the fact that more and more cars are starting to say you need to run higher grade gas. While many will say it is because the engines are better and you need to run the high grade, I still wonder what relations these two industries have.

Maybe we need the myth busters on this