The operational performance of a heated fixed-bed reactor has been studied, Previous work indicates that the distribution of heat transfer resistances is important. No generally accepted correlation exists for the wall heat transfer coefficient and the effective radial thermal conductivity, and correlations proposed in the literature have been tested and evaluated. It is found that the outer reactor tube wall temperature is very sensitive to the applied correlation for the wall heat transfer coefficient and none of the evaluated correlations match the real situation perfectly. However, the methane conversion is rather insensitive to the choice of correlation. The effective radial thermal conductivity can be determined from the assumption of equal radial heat- and momentum Peclet number. It is found that using spatially varying physical properties and gas velocities only has a minor effect an the temperature distribution. Thus, the inlet conditions can be used to determine the effect:ive radial thermal conductivity. By applying the correlation by De Wasch and Froment (1972) for the wall heat transfer coefficient, the resulting model is demonstrated for two simulation scenarios: (1) stop in steam supply and (2) stop in gas feed supply (CH4, H-2, CO and CO2). Finally, the optimal methane conversion is obtained for changing feed flow with a limiting value for the outer reactor tube wall temperature applied as a constraint.