Have you ever been confused by the different grades of gasoline offered at the pump, and wondered whether the higher grades are are actually a good investment or a total rip-off? Well you’re in luck, because in this article we’re going to help bring some clarity to this topic.

All gasoline is rated based on its octane, and the most appropriate octane for your car is definitely that which is specified in your owner’s manual. Anything lower than recommended could actually be damaging your vehicle, and anything higher is probably a waste of money. Keep reading for the reasons why…

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. In most areas of the country, regular gasoline is 87 octane, mid-grade is 89 and premium is somewhere from 91 to 93.


Almost all cars use four-­stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. For the most part, the compression ratio of your engine determines the octane rating of the gas that you must use in the car. For example, lower-octane gas (like “regular” 87-octane) can handle the least amount of compression before igniting. Higher octane gas is less combustible but that does not make it ideal for every car, by any means.

When gas ignites by excessive or extreme compression (sometimes referred to as detonation) rather than because of the spark from the spark plug, as it should, it causes knocking or pinging in the engine and this can result in damage. (What is actually happening is the pistons are rattling around inside the cylinders.) Thus, it is not something that you want to occur and though a minimal amount won’t be harmful, it’s not advisable to have much more than that. The most serious harm of detonation is the rupture of the combustion chamber, when in a worst case scenario a hole is punched through the piston or cylinder head.

There are also other factors that cause knocking such as engine deposit build-up, extremely hot weather, changes in altitude and/or hard-driving conditions, such as towing a heavy load. These conditions may result in light knocking which may not even be detected and many modern vehicles are now equipped with a device that detects and eliminates it.

There are but a few cars that absolutely require premium gasoline. Today’s engines use highly-evolved versions of a device called a knock sensor to adjust settings automatically for low-octane gas and actually are able to maximize performance on whatever grade of fuel is used.

Not only is high-grade gasoline more expensive, there is no data showing that engines designed  for regular gas run better or longer on premium. In fact, The Federal Trade Commission, in a consumer notice, emphasizes: “In most cases, using a higher-octane gasoline than your owner’s manual recommends offers absolutely no benefit. It won’t make your car perform better, go faster, get better mileage or run cleaner.” Furthermore, many petroleum companies advertise that their premium-brand gas does a superior job of cleaning engine gunk, and this is rather exaggerated. The U.S. Environmental Protection Agency requires that all gasoline, no matter the brand or the octane, contain engine detergent to prevent engine build-up.

We hope you enjoyed this post. If there is anything else we can do to help you feel free to call us at (805) 466-2446 (Atascadero) or (805) 239-8752 (Paso Robles). And be sure to stay connected with us on Facebook as well!