Computational fluid dynamics (CFD) simulations are reported for flow, diffusion, reaction and heat transfer in a 120 degrees segment of an N = 4 packed tube for the endothermic methane steam reforming reaction. The present work improves on previous approaches by explicit inclusion of intraparticle effects (conduction, species diffusion and reaction) coupled to realistic 3D external flow and temperature fields. It is shown that the usual assumption of symmetric species and temperature fields inside spherical catalyst particles holds for particles away from the tube wall, but particles placed in the strong temperature gradient near the tube wall show significant deviations. (c) 2006 Elsevier Ltd. All rights reserved.