The energy branching of the hot Io plasma torus using model calculations which include all of the significant physical chemistry that affects the system has been examined in order to study energy source characteristics. Most theoretical discussions of the energetics of the torus assume that the system is maintained against radiative and other losses by the interaction of the plasma with neutral atomic clouds. The energy in this theory is derived from the kinetic energy acquired by ions created in the rotating planetary magnetic field. Coulomb collisions with the electron gas control the flow of energy to the ionizing and radiative processes. The energetics of this theoretical system is defined by fixing the electron density, the diffusive loss time, and the relative volumetric rates of injection of the major neutral constituents, oxygen and sulfur. On the basis of calculations of this kind in comparison with the characteristics of the observed system, the conclusion has been drawn that neutral cloud theory is qualitatively inadequate. At the measured electron densities in the plasma torus neutral cloud theory can only support a dominantly singly ionized system, whereas observation fixes the ratio [S II>/[S III><1.0. The theory also fails to predict observed plasma properties relative to variations in number density. A large fraction of the energy required by the observed system based on ion partitioning alone must be derived from some other interaction. Two possibilities for energy sources involving a particular interaction with an Io atmosphere and a heterogeneous source of energetic electrons are discussed. ¿ American Geophysical Union 1988