Which refinery process separates crude oil into fractions according to their different boiling points?

Fractional distillation separates crude oil into fractions according to their different boiling points. It is the first major separation step in most petroleum refineries.

In a refinery distillation unit, crude oil is heated in a furnace and fed into a tall fractionating column. Vapors rise through the column while liquid flows downward, creating temperature zones. Lighter compounds travel higher before condensing, while heavier materials condense lower in the tower or remain near the bottom.

The resulting streams include refinery gases, naphtha, kerosene-range material, diesel-range material, and heavier gas oils and residues. These are not yet necessarily finished fuels; additional processes improve their composition and remove impurities. Fractional distillation differs from catalytic cracking, which chemically breaks large hydrocarbon molecules into smaller ones rather than merely separating existing compounds.