The electrical conductivity of Nd2O3 and Sm2O3 doped with 1 and 2 mol % CaO respectively, and LaGdO3 doped with 5 mol % BaO has been measured as a function of p(O-2), p(H2O) and temperature. Computer fitting of the data to a simple model allows determination of entropy and enthalpy terms for the defect equilibrium between water vapour, oxygen vacancies and protons, together with the pre-exponential term and the activation enthalpy of the charge carrier mobilities. The entropies and enthalpies for these and other rare earth sesquioxides are compared to those of perovskites.