How can you determine the octane rating of a substance?

The octane rating of a substance is a measure of its resistance to autocombustion when compressed. By definition, isooctane has an octane rating of 100, and n-heptane a rating of 0, and all others are in comparison to these two.

There are various ways to measure the octane rating of a substance. On way is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

For other more information, and for the source of this information, see the Wikipedia link under the Web Links to the left of this answer.