The oxygen nonstoichiometty of mixed-conducting perovskite-structured SrFe1-xMoxO3-delta (x = 0, 0.07, 0.15 and 0.25) was measured by oxygen coulometric titration in the range of oxygen partial pressure 10(-20)-0.5 atm and temperature 800-950 degrees C. Based upon a defect chemical analysis of the non-stoichiometry data it is shown that significant reduction of Mo6+ occurs under reducing conditions. The trend observed in the oxidation enthalpy suggests a weakening of the Fe-O bond strength along with the degree of substitution of Fe by Mo, which behavior is consistent with the concomitant increase in lattice constant. Atomistic simulations were carried out to support the defect chemical analysis, showing that the Mo cations in SrFe1-xMoxO3-delta retain a full, 6-fold coordination shell, whilst Fe cations can have 0, 1 or 2 oxygen vacancies in the first coordination shell. (C) 2016 Elsevier B.V. All rights reserved.