A prerequisite for any energy saving action in an industrial plant is an account of the process energy consumption. The aim is to point out steps in which the energy dissipation is great and there is a good possibility of saving energy. However, some problems still exist. For instance, how to compare thermal and electric energy units and how to measure the energy released or absorbed during a chemical process are areas in which agreement is lacking. In this paper we show how these problems can be overcome. The way here proposed of performing energy accountancy consists of considering only the active part of each energy input or output in the process, i.e., only that part of the different types of energy able to do work. During the process active energy is converted into inert energy, i.e., energy that cannot do work and. hence, can no longer be considered an economic resource.