This paper presents a numerical model (SRP) that was developed to describe the steam reforming process within tubes or channels. This model was implemented in C language and is used as a User-Defined Function (UDF) in the commercial program Fluent. The SRP model is one-dimensional representing mass and energy balances along the tubes/channels assuming uniform conditions in the cross section, except for temperature within porous regions. The model calculates the gas species concentrations and temperature profiles along the tubes/channels and since it is coupled with the Fluent furnace calculation, the boundary temperature is continuously updated and is a model result. The validation of the procedure was demonstrated by comparing the SRP model with experimental results obtained in a laboratory tubular reactor in a furnace. The SRP model was then integrated with Fluent enabling its use in the simulation of a 5 kg/day steam reformer. The reformer has a central burner within the furnace vessel that is surrounded by channels with multiple passages where the reforming reaction occurs. The model was used considering several mixtures and shows how these impacts on reformer performance. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.