Why can crude oil be separated by fractional distillation?

Crude oil is composed from hydrocarbons of varying chain length. Hydrocarbons with longer chains have higher boiling points due to the increasing strength of intermolecular forces with length, therefore the different components of crude oil have different boiling points.The fractionating column has a temperature gradient and is hotter at the bottom. Crude oil enters the column at the bottom and is heated. Intermolecular forces are broken during boiling and it is easier to break these forces between short chain hydrocarbons as they are weaker. Small hydrocarbons therefore boil more easily then travel up the column as vapour. These short molecules travel up the column the furthest before condensing, so exit nearer the top of the fractionating column. The longest chain hydrocarbons take a lot of energy to boil so condense very quickly as they rise and the temperature decreases, hence exit at the bottom of the fractionating column.