Grades of Gasoline

There are a lot of misconceptions regarding octane ratings. Fuel companies in the 60s used octane ratings as a way to present their fuel as superior. The truth is that octane ratings have a much subtler impact that some may think. Further they do not correspond to performance in the way advertising has presented them.

How Does Gasoline Make Cars Run?

Cars use combustion engines. This means they rely on the explosive properties of gasoline to push pistons that in turn spin the components connected to the tires. Burning fuel and a specific amount of air are forced into the cylinder compressing the mixture that reacts explosively driving the piston upwards where the waste air exists and fresh gas & air are forced in. 

What Is An Octane Rating?

Octane is a measurement of anti-knocking properties in gasoline. Knocking occurs when the fuel/air explodes in the wrong spot in the cylinder, producing a less optimal explosion.  There is no Octane in gasoline, nor is octane a percentage. Octane is just a measure of how well a specific gas formula performs without knocking.

What Are The Different Grades Of Gasoline?

Different grades of gasoline have different octane ratings. There are other concerns between grades, such as additives that may help the fuel burn cleaner, the biggest difference is their octane rating. The common grades are:

• Regular Gasoline: this grade of gasoline has an octane rating of between 85-88
• Midgrade Gasoline:this grade of gasoline has an octane rating of between 88-90
• Premium Gasoline: this grade of gasoline has an octane rating greater than 90

Which Octane Rating Is Best?

The octane rating isn't really better or worse. Cars are usually designed for a specific octane rating of gas. Using higher-octane gas in an engine designed for lower octane can produce waste fuel. Using low octane gas in an engine designed for high-octane fuel will result in knocking.

Does Octane Rating Effect Fuel Economy?

Using the octane rating suggested for an engine is the most optimal scenario. Knocking caused by low octane fuel results in poor performance. Using high-octane fuel, which often costs more, in a system not designed for it can result in worse mileage, as a lot of waste gas will be produced. Some engines are designed to adjust spark timing and sense when knocking is occurring. These engines can make use of varying octane levels but largely would maintain mileage performance.

Resources

The following are additional resources for understanding how gasoline grades work.

• Octane Ratings - From the Federal Trade Commission
• Alcohol Use in Fuels - The Impact of Alcohol on Octane Ratings
• What is Gasoline - Anti-knocking Agents in Fuel
• Octane & Gasoline - Get to know the Facts
• Differences in Fuel Grades - From the Department of Agriculture