Crude oil is mainly made up of chains of carbon and hydrogen atoms, called hydrocarbons. The hydrocarbon compound is the most versatile on the chemical charts – able to make an estimated 2.5 million arrangements.
Refineries use varying combinations of heat, pressure and catalysts to turn the hydrocarbon molecules in crude oil into useful petroleum products. Or to upgrade undesirable, low-value hydrocarbon compounds like fuel oil into high-value ones such as gasoline, jet fuel, diesel and naphtha.
Depending on the techniques it uses and the crude oils it buys, a refinery can be configured to produce a range of product yields, depending on demand – more gasoline in the US, for example, or more diesel in Europe.