Meaning of Octane Index

The octane index is a means of measuring the gasoline quality of certain compounds.

Therefore gasoline with a higher octane index has a higher quality and runs more smoothly. SO.........when you read 87, 89 and 91 for unleaded, superunleaded and premium at the gas station you are reading the octane index for that fuel.

Essentially, low octane fuel causes for gas mixture to explode prematurely so the cylinders in the engine do not function properly and as a result, you begin to hear you engine knock.