What is fractional distillation and how is crude oil separated into its fractions?

Fractional distillation is the separation of a mixture into its components (its fractions). Crude oil (which is made up of different hydrocarbons) is separated using a fractional distillation column. The mixture is heated to form a vapour, which is piped into the column. The column has a temperature gradient, with the top being cooler than the bottom. Hydrocarbons with high boiling points condense at the bottom and hydrocarbons with low boiling points condense on the way to the top. As the vapours condense, they form a liquid and are removed from the column as they form. Each fraction contains hydrocarbons of a similar size (similar number of carbon atoms) and similar boiling points.