Crude oil is a mixture of hydrocarbons that varies with the deposit. It varies in the relative amount of lower versus, medium, or higher molecular weight molecules. There is sweet-light crude from west Texas. Heavy crude from Venezuela, or tar from Canada.
It can all be refined(cracked and distilled). The cost of refining depends the relative mix, with the heavier the grade the higher the price.
The gasoline you put in your car is not pure octane. You have three choices of gasoline that vary with the amount of octane with the price being higher as the octane increases.