Observations of Io's torus indicate that the majority of ions have energies of 55-75 eV, with a high-energy tail extending up to the corotation energy. We have found that such a distribution can be established via the Coulomb cooling of ions heatd at the corotation energy onto the cold 5-eV electrons. The energy E* of the main body of the ions and the shape of the energy distribution are functions of the transport loss time. Matching E* with the data (E*=55-75 eV) requires transport loss times in the range 25-100 days.