The effect of hydrogen sulfide on the steam reforming of methane has been studied. Methane is the most difficult component to convert by steam reforming in the mixture of hydrocarbons, which is produced in biomass gasification. Two catalysts were subjected to hydrogen sulfide levels up to 300 ppm so as to study the effect of sulfur on their deactivation. These catalysts were the C11-9-061, from United Catalyst Inc., and the HTSR1, from Haldor Topsoe. The activation energy of the sulfur-deactivated steam-reforming reaction was calculated to be 280 and 260 kJ/mol, for each catalyst, respectively. The high values most probably originate from the fact that the degree of sulfur coverage of the nickel surface is close to 1 for these experiments. Even under these severe conditions, steam reforming of methane is possible without any carbon formation. The HTSR1 catalyst exhibits a very high sulfur-free activity, resulting in a performance in the presence of hydrogen sulfide higher than that for the C11-9-061 catalyst. By using the HTSR1 catalyst, the reactor temperature can be lowered by 60 degrees C in order to reach comparable levels of conversion.