The performance of a novel gasoline steam reformer with facing catalytic burner and reformer both based on the microchannel concept (system A) was modeled and then compared with a reference catalytic SR reactor facing, as the heat source, a microchannel heat exchanger fed with the flue gases from an external burner (system B). Reactions in the catalytic reformer and the catalytic burner occurred heterogeneously on Pt-CeO2 catalysts. The developed dynamic model [25 partial differential equations (PDEs) for system A; 15 PDEs for system B; reforming and combustion kinetics from the scheme proposed by Pacheco et al. (Appl. Catal. 2003, 250, 161)] was numerically solved. The simulation results showed that the integrated burner-reformer microchannel reactor (system A) was able to transfer heat from the hot side to the cold side very efficiently, thus enabling high compactness. However, the best design conceived (the catalytic burner facing toward the reformer microchannel) showed mass-transfer limitations inside the burner catalyst layer because of the low values of the effective diffusion inside the solid catalytic phase. As a consequence, there was not an "ignited" condition in the catalytic burner (confirmed by the lack of a peak in the burner temperature profile) but a diffuse heat generation along the microchannel length. This condition involves a longer reformer start-up but at the same time allows one to limit the temperature increase in the catalyst solid layer, preserving its activity and stability. From the dynamic analysis, a longer start-up time resulted for system A, which could be a limitation for automotive applications. Conversely, this system proved to guarantee a fast response to sudden load changes: hydrogen production reached almost instantaneously the new steady-state conditions, as needed for vehicle applications.