A new anode micromodel for solid oxide fuel cells to predict the electrochemical performance of hydrocarbon-fuelled porous composite anodes with various microstructures is developed. In this model, the random packing sphere method is used to estimate the anode microstructural properties, and the complex interdependency among the multicomponent mass transport, electron and ion transports, and electrochemical and chemical reactions is taken into account. As a case study, a porous NiYSZ composite anode operated with biogas fuel is simulated numerically and distributions of the current density, polarization, and mole fraction and rate of flux of the fuel components along the thickness of the anode are determined. The effect of the anode microstructural variables including the porosity, thickness, particle-size ratio, and particle size and volume fraction of Ni particles on the anode electrochemical performance is also studied. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 18931906, 2012