There is growing interest in developing oxide materials for direct hydrocarbon solid oxide fuel cell anodes. In addition to electronic and ionic conductivities, the electrocatalytic activity of these materials is a critical requirement for a high performance anode. In this paper, we present evidence for the important role of variable lattice oxygen stoichiometry and anode geometry in dictating the activity and reaction mechanism of La(0.75)Sr(0.25)Cr(1-x)Mn(x)O(3-delta)-based anodes for CH(4) oxidation. Total oxidation of CH(4) is favored by low oxygen vacancy concentration and availability of reducible B-site cations. The non-linear dependence of electrode polarization resistance with current density is attributed to dynamic changes in lattice oxygen vacancy concentration. The relatively high open circuit potential of porous anodes compared with thin films is attributed to an increase in secondary reactions of the fuel within the porous anode. (C) 2010 Elsevier B.V. All rights reserved.