A bench-scale annular microchannel reactor (AMR) prototype with microchannel width of 0.3 mm and total catalyst length of 9.53 x 10(-2) m active for the endothermic steam reforming of methane is presented. Experimental results at a steam to methane feed molar ratio of 3.3:1, reactor temperature of 1023 K, and pressure of 11 bar confirm catalyst power densities upwards of 1380 W per cm(3) of catalyst at hydrogen yields >98% of thermodynamic equilibrium. A two-dimensional steady-state computational fluid dynamic model of the AMR prototype was validated using experimental data and subsequently employed to identify suitable operating conditions for an envisioned mass-production AMR design with 0.3 mm annular channel width and a single catalyst length of 254 mm. Thermal efficiencies, defined based upon methane and product hydrogen higher heating values (HHVs), of 72.7-57.7% were obtained from simulations for methane capacities of 0.5-2S LPM (space velocities of 195,000-782,000 h(-1)) at hydrogen yields corresponding to 99%-75% of equilibrium values. Under these conditions, analysis of local composition, temperature and pressure indicated that catalyst deactivation via coke formation or Nickel oxidation is not thermodynamically favorable. Lastly, initial analysis of an envisioned 10 kW autothermal reformer combining 19 parallel AMRs within a single methane-air combustion chamber, based upon existing manufacturing capabilities within Power & Energy, Inc., is presented. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.