A mathematical model of the reformer sponge iron cycle (RESC) is presented. The model is based on a thermodynamic analysis of the process, simulating the complete hydrogen production cycle including the hydrocarbon reformer, the sponge iron reactor (SIR) and the auxiliary devices required to operate the process. A parametric process analysis is performed in order to investigate the effect of different levels of operating temperature and different recycle rates on the RESC system performance. A number of gaseous and liquid hydrocarbons are investigated as candidate fuels for applications requiring an on-site hydrogen production capacity. Hydrocarbon to hydrogen conversion efficiencies are presented, along with a full analysis of mass and energy balances. An additional hydrocarbon burner unit running with the same fuel as the RESC hydrogen production cycle is considered as heat source for the endothermic conversion process of hydrocarbon fuel into hydrogen. The mathematical RESC model provides a sound base for further developments of the system, and will be applied in theoretical studies performed in parallel to investigations with a laboratory-scale unit operated at Graz University of Technology. (c) 2006 Elsevier B.V. All rights reserved.