A protocol for the inexpensive fabrication of catalytic microburners with integrated thermocouples is introduced. Experimental data for the oxidation of hydrogen/air mixtures over platinum/ alumina microchannels of different channel gap distances is presented. Lean hydrogen/air mixtures are found to be self-igniting, and no detectable fuel-lean limit for autothermal (self-sustained) operation is observed. The role of microreactor gap size (confinement) in enhancing transport rates and changing the dominant chemistry is experimentally demonstrated for the first time. Evidence of homogeneous combustion is found for near-stoichiometric hydrogen/air mixtures in 1000-mum-gap reactors, but not in 250-mum-gap reactors. Spatially resolved temperature profiles indicate significant longitudinal nonuniformity. Finally, catalytic and homogeneous microburners are briefly contrasted.