A refinery's return on investment is a measure of profitability of the refinery relative to the amount of capital tied up in it. Refineries are very capital intensive businesses and require high operating profits to earn a reasonable return on capital.

The capital employed in a refinery is primarily comprised of:

PP&E (property, plant and equipment) - Value of process units, land and supporting infrastructure such as roads, buildings, tanks, etc

Hydrocarbon inventory - Value of crude oil, intermediates and products held in inventory in the refinery

Equipment inventory - Value of spare equipment stocks required to maintain the refinery