The activity test of commercial catalysts of steam-hydrocarbon reforming was carried out under the wide range of working conditions（T=650∼850^oC; S.V.=600∼1,200 hr^-1; steam to carbon ratio=1.17）.
An activity test method has been developed through the parallel-triple-column gas chromatographic technique.
The following results were obtained:
（1） Hydrocarbons are scarcely found in the outlet gas except methane, and the gas composition could be approximately predicted by assuming the chemical equilibrium at the reaction gas temperature, among H₂, CO, CO₂, CH₄, and H₂O.
（2） It is difficult to compare the activity of catalysts by any direct comparisons of kinetic data at the high conversion level of reactants, while a conventional method proposed by Inoue et al. is eligible.
（3） It was concluded that the activity of commercial catalysts A, B, and C are approximately same.
（4） Steam to carbon ratio to prevent the carbon deposit was examined experimentally and theoretically.