We present a method for determining the thermodynamic effectiveness of energy use in individual processes, large-scale productions and the national economy as a whole. The theoretically required minimal energy/exergy consumption is used to calculate process effectiveness in energy-consuming branches. Applications include processes involving chemical transformations, deformation in rolled-stock production, space heating, and hot water supplies. Energy and exergy efficiencies are also estimated for ferrous metallurgy and for the economy of the former U.S.S.R.