Answer. Refining process is the separation of crude oil mixture into various useful products (fractions). It is carried out by a process called fractional distillation in a fractionating tower. The crude oil is heated in a furnace up to a temperature of 400°C under high pressure. Then vapours are passed through a fractionating column from near its bottom, hot vapours rise up in the column and gradually cool down and condense. Such that vapours of higher boiling point fraction (350— 400°C) condense first in the lower part of the tower, while vapours of medium and lower boiling point fractions rise upwards in the tower and condense gradually with respect their boiling points at different levels. In this way crude oil is separated into six hydrocarbon fractions as discussed below. Each fraction has its specific boiling range, composition and uses.