Roughly half of today's vehicles are equipped with knock sensors. Most cars give optimum performance on regular or mid-grade gasoline. If you're buying premium and your car's not running any better than it does with a lower-octane gasoline, you're probably wasting money. However, some cars may operate better on premium because of additives. Additives, which are found in all gasolines, keep engines clean and make them run more efficiently.
Some brands have more effective additives and some use bigger doses in their premium grades.
Driving habits, a vehicle's mileage, and climate and geography can affect how gasoline performs in your car. Octane requirements tend to increase with mileage, at least through the first 15,000 to 20,000 miles. And a car hauling heavy loads over hills requires more octane than the same car driving on level roads. On the other hand, many older vehicles need less octane at higher altitudes, such as the Rocky Mountains. The octane level recommended by your vehicle's manufacturer is a good starting point.