The difference between grades of fuel is the octane number and to a small degree the additive packages. The difference in additive packages between grade is not as significant as it once was.
There is no advantage of using a higher octane fuel than what the manufacture recommends for the car unless the engine spark knocks, then move up a grade. Generally speaking though, as a car ages and more miles on the engine, you may find that you will have to move up a grade of fuel because the engine has started spark knocking.
One thing most people don’t know is that ethanol boosts the octane of fuel and is can be as prevalent in premium grades as in lower grades, a cheap way to boost the octane number, especially if a refinery’s power former is limited, and therefore isn’t producing enough octane to meet gasoline grade demands.
