The fractions of crude oil are best separated by fractional distillation because the different hydrocarbons have different boiling points.

In this process, Crude oil is heated and vaporized. The vapour rises through a tall fractionating column which is hot at the bottom and cooler at the top.However, different fractions condense at different temperature levels (heights) in the column and are collected separately. Then, lighter fractions with lower boiling points condense at the top, while heavier fractions with higher boiling points condense at the bottom.