The fixed-bed oxygen absorption processes of the series of Ba1-xSrxCo0.8Fe0.2O3-delta oxides were studied by oxygen partial pressure swing absorption in the temperature range of 300-850 degrees C. The results show that Ba1-xSrxCo0.8Fe0.2O3-delta, with the smallest A-site ion radius, has the largest oxygen absorption capacity (0.402 mmol/g) at 500 degrees C. The oxygen absorption and desorption kinetics fit well with the pseudo-second-order kinetics model. Comparing the modeling absorption rate coefficient k(2) with the desorption rate coefficient k(2)', all the oxides studied had higher oxygen absorption rates than oxygen desorption ones. In addition, the combined results of X-ray diffraction analysis, O-2-TPD, room temperature iodometric titration, and thermogravimetric analysis explained the relationship between the oxygen absorption capacities and the average radii of the A-site ions for this series of Ba1-xSrxCo0.8Fe0.2O3-delta in the temperature range of 300-600 degrees C. (C) 2009 American Institute of Chemical Engineers AIChE J, 55: 3125-3133, 2009