The interaction of oxygen in the gas phase with double perovskites LnBaCo(2)O(6 - delta) (Ln = Pr, Sm, Gd) was studied by the isotope exchange method with gas phase equilibration in the temperature range of 600-850 degrees C and the oxygen pressure range of 1.3 .10(-3)-6.6.10(-2) atm. The oxygen nonstoichiometry of the oxides was determined by means of the thermogravimetric analysis as a function of oxygen partial pressure and temperature in the ranges -3 <= log(Po-2/atm) <= -0.68 and 600 <= T, degrees C <= 850, respectively. The influence of the oxygen nonstoichiometry on the heterogeneous exchange rate and the oxygen tracer diffusion coefficient was discussed. The rate-determining stage of the oxygen surface exchange kinetics for PrBaCo2O6 (-) (delta) was found to be different in comparison with SmBaCo2O6 (-) (delta) and GdBaCo2O6 (-) (delta). The possible reasons of this observation were considered. (C) 2017 Elsevier B.V. All rights reserved.