Why do gas stations have three different grades of gas?

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Why do gas stations have three different grades of gas?
Gas stations typically have at least three different kinds of gasoline and then usually at least one kind of diesel. The three grades of gasoline are 87 octane, 89 and 91, or variations thereof. Octane ratings are sort of a perfomance standard for gasoline. It's a rating that reflects the ablility of the gasoline to help your engine resist knocking or pinging, a very traditional kind of sound that you hear when there's incomplete combustion in the engine. And the vast majority of cars produced for sale in the United States are designed to run on 82 octane gasoline or less, and yet you'll notice that the lowest octane gasoline you can buy in most stations is about 87. So having higher octane gasoline for sale is really a kind of fraud, especially when it's promoted, as it is by most oil companies, as being something that everyone can benefit from.The truth is high octane gasoline is really only designed to be used by high performance, high compression engines like a 12-cylinder Maserati. The Federal Communications Commission and other government agencies have found oil companies guilty of misrepresentation and fraud for trying to tell the public otherwise.