There are different types of crude oil extracted from the ground and given labels like heavy, light and sweet. This means it contains different proportions of different hydrocarbons this oil is then processed by fractional distillation separating out the various hydrocarbons in crude oil by their different boiling points. The longer chains of hydrocarbons can also be cracked into shorter chains to produce more useful chemicals. – https://youtu.be/BCfw4S8c3b8
So some of the hydrocarbons are used to make heating oil, fuels for cars or making plastics, depending on what a country has and needs they will trade them.
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