Conventional steam methane reformers operate with contact times exceeding I s. Recent literature has suggested that microchannel reactors may reduce the contact time to a few or tens of milliseconds. This report shows both experimentally and theoretically that the I ms barrier for steam methane reforming (SMR) has been broken with the aid of a tailored microchannel reactor design, where the catalyst is coated on a relatively thick porous engineered structure. While I ms contact time reactions have been approached by the partial oxidation of methane to synthesis gas, steam reforming has historically been considered a slow reaction. Methane steam reforming experiments at contact times of 90-900 mu s were conducted. Greater than 98% approach to equilibrium methane conversion was demonstrated at 900 mu s, and 19.7% approach to equilibrium was measured at 90 mu s. Both cases were supported with good model agreement. Further, the model explores microchannel reactor structures that minimize heat and mass transfer and results suggest that at a contact time of 500 mu s a high approach to equilibrium is possible. (c) 2006 Elsevier B.V. All rights reserved.