The oxygen transport in La1-xSrxFe1-yMnyO3-delta (LSFM) with 0 less than or equal to x less than or equal to 0.5 and y = 0.2 and 03 has been examined with a thermogravimetric method. As long as x less than or equal to y, the oxygen transport was found to be very slow while the oxygen transport increased several orders of magnitude when x > y. For two compositions-La0.5Sr0.5Fe0.7-Mn0.3O3-delta (1) and La0.6Sr0.4Fe0.8Mn0.2O3-delta (II)-oxygen chemical diffusion coefficients were determined and found to increase from 1.5 x 10(-5) to 5.6 x 10(-5) cm(2) s(-1) for composition (1) and from 1.4 x 10(-6) to 1.4 x 10(-4) cm(2) s(-1) for composition (11) in the temperature range 750-1000 degreesC. The activation energy for the oxygen chemical diffusion was found to be 66 U mol(-1) for La0.5Sr0.5Fe0.7Mn0.3O3-delta and 136 U mol(-1) for La0.6Sr0.4Fe0.8Mn0.2O3-delta. The oxygen surface exchange constants were found to vary between 2.5 x 10(-4) and 1.8 X 10(-2) cm s(-1).