The kinetics of methyl radical production on 1% Sr/La{sub 2}O{sub 3} has been studied by using a heatable tubular flow reactor, containing the catalyst, coupled to a photoionization mass spectrometer. The experimental technique, which permits direct detection of stable species and free radicals and measurements of their absolute concentrations along the reactor, is described. Experiments were conducted using conditions which isolated the initial CH{sub 3}(g) production step. Absolute rates of CH{sub 3}(g) production were determined from measurements of CH{sub 3}(g) concentration profiles along the reactor. Rates were measured as a function of T (982{minus}1,138 K), (CH{sub 4}(g)), and (O{sub 2}(g))/ The information obtained was used to deduce the rate law for methyl radical production and to identify the most likely kinetic mechanism of this process. The body of data obtained and the rate law indicate the establishment and maintenance of an equilibrium between O{sub 2}(g) and surface-bound oxygen atom. The temperature dependence of the constants in the rate law indicates that {Delta}H{degree} = 44 {plus minus} 10 kcal mol{sup {minus}1} for the endothermic adsorption (O{sub 2}(g)) {yields} 2({minus}O(surface)), and the activation energy for the gas-surface reaction responsible for the production of CH{sub 3}(g) is 21 {plus minus} 5 kcal mol{supmore » {minus}1} (CH{sub 4}(g) + {minus}O(surface) {yields} CH{sub 3}(g) + HO(surface)). Heterogeneous loss of CH{sub 3}(g) did not occur to an observable degree under the conditions of these experiments.« less