The available literature information on the phase equilibria for the La-Ga-Ni-O system has been assessed. Based on the known thermodynamics of boundary oxygen containing systems, La-Ni-O, La-Ga-O, and Ga-Ni-O, and experimental data on phase equilibria in the La2O3-Ga2O3-NiO quasiquatemary system, models have been defined to describe the Gibbs energy of the individual phases. The model parameters have been optimized by least-squares fit to selected experimental information using the CALPHAD-method (Calculation of Phase Diagrams). Chemical potential diagrams of the systems representing fabrications and cathode-anode side operation conditions of LaGaO3-based solid oxide fuel cells (SOFC) were calculated. It has been determined that, neither in fuel cell fabrication conditions nor in operation conditions un-doped LaGaO3 electrolytes and La2NiO4 cathodes are stable in equilibrium with each other but will react to form another phases. (c) 2006 Elsevier B.V. All rights reserved.