Medium lubricating oil being poured from a bottle. Lubricating oil is a product of the refining of crude oil. Crude oil is a mixture of hydrocarbons that is heated to separate it into parts called fractions. The lighter hydrocarbon fractions boil off and leave the heavier fractions behind. Lubricating oil contains hydrocarbon chains with 20-50 carbon atoms, with medium lubricating oil in the middle of this range with a medium viscosity. Lubricating oil boils in the range 300-370 degrees Celsius, and is used to lubricate motor vehicles and industrial machines.