This paper presents both experimental and modeling investigations of a catalytic wall fuel processor consisting of coupled methane reforming and methane combustion sections. The reacting systems are both catalytic and the latter generates the heat required for the occurrence of the former. The catalytic wall reactor was examined for light-off behavior and for steady-state product distribution. On one hand, the analysis of the reaction products distribution after catalyst ignition indicated that in both combustion and reforming sections catalysts undergo to a relatively long transient (about 40 min) before reaching steady state conditions. On the other hand, a much longer reactor thermal transient was observed and the two transient behaviors appear independent of each other. Analysis of the reactor operating under real conditions (nonadiabatic) showed that a 3D model is needed to accurately predict the reactor performance because a 2D model, although much more convenient, cannot allow for the whole heat loss thereby yielding unreliable results.