Have you ever borrowed a friend’s car only to find out there’s no gas in it, and it only runs on premium? Many turbocharged cars and some naturally aspirated performance cars require only the good stuff, but what about using premium in your car even if the manufacturer doesn’t require it — are there any gains to be had? Could the better fuel result in increased mpg?
The answer is complicated. In most practical cases, it’s no, but, to fully understand why you’re better off buying regular, you’ve got to understand what makes premium gas premium and where exceptions to the rule make using premium the better choice.
The major differentiator between premium and regular fuel is its octane rating. Maybe you’ve heard references to “high-octane” and figured they had something to do with race cars, and that’s true, but Tony Stewart doesn’t buy gas for his NASCAR at the local 76. Even the highest-octane fuel you’ll get from a gas station is only a few points higher rated than regular.
Octane is a measure of how stable fuel is under compression. Higher-octane fuels can withstand higher pressure without combusting on their own, which is why you must use them in high-compression applications like sports cars.
The highest-octane premium fuel you can buy in the USA at normal gas stations is 93 octane. Regular grade typically runs at about 87 octane, so you’re only talking a difference of five points, and that’s outside of California where you’re stuck dealing with 91-octane premium.
WHEN OCTANE MATTERS AND WHEN IT DOESN’T