Millions of drivers likely don’t pay much attention to what difference different kinds of gas can do for their car. If you are like most drivers, you typically go to the same gas station or the same brand, if you’re traveling. You buy the same type of gas on each occasion. You may be swayed by prices and use or an app from AAA or another source to find the least-expensive gas prices in your area. But do you really know what different types of gas do for your car? The answers may or may not be surprising.

The first point to remember is that, for the most part, it doesn’t matter what kind of gas you put in your car. Most cars are designed to work perfectly fine on economy gasoline. In fact, many auto experts say that putting a premium grade of fuel in a car that calls for economy gas is like gussying up a pig or giving a treat to a dog. You’re not going to get any more benefits out of the effort (other than perhaps feeling good about doing it) and it will cost more.

Some cars, however, run most efficiently and perform better when a higher octane gas is used, also called premium-grade or high-performance gasoline.

What is the big deal about octane? Is it octane that should be considered, rather than different types of gas?

Octane comes in different ratings. Generally speaking, the higher the octane rating specified on the pump choices, the slower the ignition or burn. While most gas stations in the U.S. offer octane ratings ranging from 87 to 92, the most commonly-used octane rating is 87. That is because, once again, most cars are designed to run on regular unleaded fuels with an 87 octane rating. An 87 octane rated gas is generally cheaper than a higher octane rating.

Some older cars may also require a higher octane.

For cars with high-performance engines, including those with turbocharging, a higher octane gas may be required and, indeed, is recommended by the auto manufacturer for the vehicle. If lower octane gas is used in place of the recommended premium or higher octane rated gas, engine knocking or pinging may occur or the car may display less-than-desired performance.

Note that the different types of gas – economy or regular 87 octane, or 89 to 93 octane rating – do not include diesel fuel or bio-diesel fuel. Using those types of fuels in a car designed to run on gasoline will wreck the engine.

How do you know what kind of gas or the octane rating recommended for your car? The best bet is to look for documentation in your car’s owner’s manual. If your car requires a higher octane rating of 89 to 93, this rating requirement may also be specified under the fuel gauge and near the fuel fill hole.

What about reformulated gasoline? In some areas of the country or specific locales with air pollution problems, reformulated gasoline is required. In California, for example, reformulated gasoline is sold during the summer months. In essence, reformulated gasoline is an oxygenated fuel that burns clan but can slightly lower fuel economy and engine performance. Very dirty engines with carbon deposits may begin knocking and pinging or premature burn with use of reformulated gas. In such situations, some auto experts suggest that switching to a higher octane or the next grade up of gasoline may help.

Bottom line: It isn’t Shell versus Exxon or Texaco or Mobil or any other major gasoline brand that makes a difference. Use the type of gasoline (the octane rating) recommended by the manufacturer of your vehicle. If you believe that diesel or hybrids or flex-fuel vehicles offer better performance and less pollution than gasoline engine-powered vehicles, consider making a switch to that type of vehicle the next time you buy a car.

Keep in mind, though, that all auto manufacturers are racing to improve fuel efficiency and reduce emissions in gasoline engines and are making considerable strides with each new engine and vehicle redesign.

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