A numerical study is performed to evaluate the effectiveness factors of commercial nickel catalyst pellets commonly used in small-scale steam methane reformers for residential fuel cell applications. Based on the intrinsic reaction kinetics of the steam reforming process, the standard composition of the partially reformed gas mixture is determined as a function of the methane conversion. The heterogeneous reforming reactions inside the spherical catalyst pellets are then modeled by considering the distributed reaction, multicomponent diffusion and permeation, and conductive and convective heat transfer in the porous media. Various operating conditions, including the reforming temperature, steam-to-carbon (S/C) ratio, operating pressure, and geometrical parameters, such as the pellet diameter and mean pore size, are simulated. The effectiveness factors calculated for each condition are presented as a function of the methane conversion. Finally, simple correlations for the effectiveness factors are presented, and their accuracies are assessed. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.