Catalytic steam reforming of a model biogas (CH4/CO2 = 60/40) is investigated to produce H-2-rich synthesis gas. Gas engines benefit from synthesis gas fuel in terms of higher efficiency and lower NOx production when compared to raw biogas or CH4. The process is realized in a fixed bed reactor with a Ni-based catalyst on CaO/Al2O3 support. To optimize the performance, the reactor temperature and the amount of excess steam are varied. The experimental results are compared to the theoretical values from thermodynamic calculation and the main trends of CH4 conversion and H-2 yield are analyzed and verified. Finally, optimal reactor temperature is pointed out and a range of potential steam to methane ratios is presented. The experimental results will be applied to design a steam reformer at an existing anaerobic biomass fermentation plant in Strem, Austria. (C) 2007 Elsevier Ltd. All rights reserved.