The index of the process energy efficiency has been introduced to assess the energy efficiency of oil refinery units and their complexes. The index is calculated as the ratio of the payload difference of the hot utilities of the operational unit and the reference unit to the payload of the operational unit. As a reference unit, the examined unit is selected with a thermal energy recuperation system, which has a specified value of driving force for vertical heat transfer. This value of the minimum temperature difference of the heat transfer carrier in the heat-exchange equipment is selected using the best available technologies in heat transfer. Additionally, the energy efficiency index is calculated taking into account the elimination of heat losses to the environment. A simplified method for estimating heat losses from heated surfaces of oil refinery equipment has been developed for this purpose. It is shown that to determine the energy efficiency of a unit complex, it is possible to use the temperature Total Site profile. Indices of energy efficiency for crude oil unit, catalytic reforming with preliminary hydrotreating for the production of stable catalysis unit and hydrotreating of diesel fuel and kerosene unit, as well as their complex, are determined. Indices for economically optimal integration of these processes are decided. The introduced index of the energy efficiency potential of the process is an absolute value indicating the grade of the process perfection. The introduced index can be used to compare the energy efficiency of both individual units and plants.