What does the octane rating of gasoline tell you about the gasoline? where can you see the octane rating of the gasoline you buy?

Explanation:

The Octane rating is the % Octane in the grade that you are buying. In the United States, the octane rating of the cheapest gas is around 85%. In Canada, it is about 87% which in the states is the mid grade.

As soon as you take out the nozzle from its container, you have to press a large colored button to pick the octane rating. The button is so large and the writing is so limited, that you cannot miss the grade. Usually they are put together on the pump like this

87  89  91

I've given you the Canadian numbers; I'm not sure what they are in the US, but the numbers I've used are pretty close.