Experimental data on oxygen desorption from barium cerates doped with neodymium together with data on equilibrium saturation of cerates by oxygen were used for mathematical modelling of oxygen nonstoichiometry of the oxides as a function of P-O2. Such sorption parameters as ks(0) and Q were determined by iterative fitting of experimental with calculated data and good agreement of experimental and modelled data confirms the adequacy of proposed model. It was also fond that LaMnO3 doped with strontium has a tendency to interact with carbon dioxide during sample annealing in air. (C) 2003 Elsevier B.V. All rights reserved.