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The Differences in Gasoline

Sometimes the choices at the pump can be confusing, especially when terms change from station to station. If you want to understand the important differences between these gasoline choices, read on.

Octane and Grades of Fuel
Octane is not a measurement of power. Octane ratings are a measurement of the fuel's ability to resist engine knocking or pinging. The knock results from uneven burning of the compressed fuel-air mixture. Michigan law requires that each grade of gasoline be consistent in octane. There are standardized grade names so consumers can readily identify the grade and the octane of the gasoline. Regular is 87 octane; Midgrade and Premium grades are required to have the octane rating as part of the name (i.e. Premium 93). Stations are required to post the grade names on the pumps in a location readily visible to the consumer. Check your owner's manual to determine which octane is recommended for your car. You will not need a higher-octane gasoline if your car engine runs without making a pinging or knocking sound. Using gasoline with too low an octane rating can result in engine damage. Octane requirements may increase with the age of a vehicle. Vehicles pulling heavy loads may also require a higher octane to avoid engine knock.

Ethanol Fuels
Ethanol has been used as an octane enhancer in Michigan gasoline for many years. Adding ethanol to the gasoline increases the octane almost 3 Anti Knock Index points. Not all gasoline contains ethanol. If ethanol is in the gasoline, it is limited to no more then 10 percent of the total volume for conventional fuels.

Methyl Tertiary Butyl Ether (MTBE) is a chemical compound that is used as a fuel additive in gasoline. MTBE is a gasoline additive that was also used in limited quantities in Michigan as an octane enhancer. Because of ground water concerns, MTBE is banned from use in Michigan gasoline with almost none being detected in Michigan gasoline today.

Fuel Additive Packages
All gasoline sold in Michigan is required to meet a minimum fuel performance standard established by the state.

All gasoline sold in the United States is required by the EPA to have a minimum level of fuel additive to prevent fuel injector clogging.

The major differences in gasoline result from the fuel additive packages that go beyond the minimums established and the degree of quality control measures that some marketers have put in place to ensure a consistent high quality product.

Some of these additive packages are designed to not only keep the engine clean but also clean up a dirty engine/fuel injectors/ and prolong the life of the engine, etc. Since these additives are very expensive to add to the gasoline, many of the major oil companies do their own testing of the gasoline at retail to make sure it is their additive package that is being used and that the fuel has not been altered or modified by an unscrupulous dealer trying to increase profits.

Because Michigan has a Motor Fuels Quality program, every gasoline sold in this state should meet the minimum standards and perform satisfactorily in the average consumer's vehicle provided they have purchased the recommended octane. The added benefits that some marketers offer is a matter of consumer preference based upon their vehicle needs and driving experiences. If a particular vehicle performs best on one type of gasoline, you may wish to stick to that type for best engine performance and longevity.

Should you have questions or concerns regarding the quantity or quality of gasoline you have received, please contact the Michigan Department of Agriculture & Rural Development, Consumer Complaint Toll Free Hotline at 1-800-MDA-FUEL.

For more information on Michigan gasoline, check out the MDARD's Michigan Gasoline Corner web page.