The effect of catalyst temperature on the partial oxidation reaction pathways of methane over platinum is investigated in a stagnation-flow reactor. A new experimental method is described that uses Raman spectroscopy to measure the concentration of CH4 along the centerline of the reactor with the Pt surface at 900-1100 degreesC. The method permits the direct comparison of the measured reactivity with that predicted by the CHEMKIN SPIN stagnation-flow code when combined with recently developed partial oxidation elementary reaction mechanisms. A significant increase in the reactivity of CH4 on Pt is observed between 1000 and 1100 degreesC, concurrent with an increase in the selectivity to H-2 and CO. No single mechanism available in the literature correctly models the increase in reactivity or the change in selectivity in this temperature range. The experimental results are interpreted by examining the competitive adsorption between CH4 and O-2 and the two pathways by which CH4 can undergo dissociative adsorption. The temperature dependence of the sticking coefficient for the direct dissociative adsorption of CH4 is specifically identified as an important yet highly uncertain parameter in the reaction mechanism.