The kinetics of methanol steam reforming on a commercial CuO/ZnO/Al2O3 catalyst in packed-bed and wall-coated microreactors were compared experimentally. Different dimensions of both reactor configurations were tested and the transport limitations were analyzed using 2D reactor models. Packed-bed reactors of dimensions from 4.1 down to I mm i.d. were found to be heat transfer limited and temperature gradients of up to 40 K could exist in the bed. The reactor diameter required to eliminate temperature gradients was estimated to be 300 mu m, which clearly is not practical. On the other hand, the wall-coated reactor was found to be free from any mass or heat transfer limitations in dimensions from 4.1 mm down to 200 mu m i.d. Our modeling results showed that the reactor volumetric productivity increases with thicker catalyst wall-coatings for the same reactor diameter. We also show that the wall-coated reactor offers a better solution to achieve low pressure drop and high catalyst activity compared to a packed-bed microreactor. (c) 2005 Elsevier B.V. All rights reserved.