The operational performance of a heated "xed-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 coe$cient and the e!ective radial thermal conductivity, and correlations proposed in the literature have been tested and evaluated. It is found that the outer reactor tube wall temperature is very sensitive to the applied correlation for the wall heat transfer coe$cient and none of the evaluated correlations match the real situation perfectly. However, the methane conversion is rather insensitive to the choice of correlation. The e!ective 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 e!ect on the temperature distribution. Thus, the inlet conditions can be used to determine the e!ective radial thermal conductivity. By applying the correlation by De for the wall heat transfer coe$cient, the resulting model is demonstrated for two simulation scenarios: (1) stop in steam supply and (2) stop in gas feed supply (CH , H , CO and CO ). Finally, the optimal methane conversion is obtained for changing feed #ow with a limiting value for the outer reactor tube wall temperature applied as a constraint.