The oxide stoichiometry of La1-xSrxCo1-yFeyO3-delta perovskite powders was investigated by means of solid electrolyte coulometry. Experiments were performed at reduced oxygen partial pressures between 1.3 x 10(-3) atm and 6x 10(-5) atm, applicable to cathodic bias under solid oxide fuel cell operating conditions. It was found that the degree of oxygen non-stoichiometry (delta) increased with increasing temperature, decreasing oxygen partial pressure and increasing Sr or Co content. Transient re-equilibrium experiments, following a small perturbation in the temperature or oxygen pressure, were carried out to investigate the oxygen transport and surface absorption kinetics. Using a suitable diffusion model and non-linear parameter optimization, the surface exchange coefficient (k) and chemical diffusion coefficient (D) of oxygen were obtained from the transients. The results were found to be consistent with those of other relaxation techniques.