The heterogeneous reaction of hydrogen and methane with graphite in a flowing gas stream system above 1600 K was examined by a phenomenological analysis and was found to give a one-half-order back reaction based on large additions of methane to the feed stream. A reaction mechanism that involves a slow step with rearrangement on the surface, followed by a fast step with two of the product species from the slow step combining to form methane, results from the analysis. Qualitative flow effects were observed. Measurements were made at 12.9 atm absolute.