As fractional distillation method is used for the separation of a mixture of two or more miscible liquids with a difference in boiling points of less than 25 K.

This apparatus is almost similar to that used for simple distillation, except that between the distillation flask and the condenser is a fractionating column.

As components of petroleum have differences in boiling points of less than 25 K, fractional distillation can be used to separate distinct components from petroleum.