Thermogravimetric analysis and a coulometric titration technique were used to measure the relative changes in oxygen stoichiometry of Sr-0.97(Ti,Fe)O3-delta materials with temperature and oxygen partial pressure, and these results were used to re-examine the defect chemistry. These materials undergo significant weight gain on cooling which was attributed to changes in valence of Fe ions. The oxygen gain attained on cooling from 1300 degreesC to room temperature indicates that Fe3+ and Fe4+ coexist in these materials, and that the concentration of oxygen vacancies remains relatively high in wide ranges of working conditions but may vary with temperature, and/or oxygen partial pressure. (C) 2000 Elsevier Science B.V. All rights reserved.