The Calphad method was used to perform a thermodynamic assessment of the Pr-O system. Compound energy formalism representations were developed for the fluorite -PrO2-x and bixbyite sigma-Pr3O5 +/- x solid solutions while the two-sublattice liquid model was used to describe the binary melt. The series of phases between Pr2O3 and PrO2 were taken to be stoichiometric. Equilibrium oxygen pressure, phase equilibria, and enthalpy data were used to optimize the adjustable parameters of the models for a self-consistent representation of the thermodynamic behavior of the Pr-O system from 298K to melting.