Microprobe mass-spectrometric sampling is used to measure major species in a stagnation-point flow over a heated La0.267Sr0.333Mn0.4Al11O18 hexaaluminate catalyst surface. The temperature of the catalytic surface is controlled, and the flow is composed of high-purity methane and air. A chemically-reacting flow model with a global surface-reaction mechanism and GRI-Mech 3.0 gas-phase chemistry is developed and used to assist interpretation of the experimental data. Comparison of experimental data with numerical models that include both surface and gas-phase chemistry suggests that the catalyst surface tends to quench gas-phase combustion by removing methyl radicals. Over a range of conditions, surface temperature (680degreesC less than or equal to T-s less than or equal to 1110degreesC), and equivalence ratio (0.2 less than or equal to phi less than or equal to 0.4), the numerical model is able to achieve good agreement with the measurements. (C) 2003 The Combustion Institute. All rights reserved.