How is petroleum refined?

Petroleum is "cracked" as they call it from it's state found in nature. In nature, petroleum can take the form something as light a gas, or as heavy as tar, and everything in-between.

What people commonly think of as petroleum is oil. VERY SIMPLY, oil is heated in a very tall, very narrow tank. The heavest portions of the oil "kerosen" come out at the bottom, then diesel, then gasoline. Heating the oil helps to separate the crude oil out into its separate components. The amount and ease to which crude oil is "cracked", or, refined, is dependent on how many carbon atoms are in it's molecular structure. The fewer, the lighter weight -- like natural gas. the more carbons, the more like tar it is.