1-Methylnaphthalene exhibits first-order decay during early extents of oxidation in a flow reactor at approximately 1200 K. Using temporal profiles of measured stable intermediate species and reaction path analysis,estimates are made of the radical species mole fractions that necessarily exist near steady state under these conditions. The radical estimates are found to be similar to previous estimations and computations of radical mole fractions in the flow reactor oxidation of toluene, the, monocyclic aromatic analog of l-methylnaphthalene. Computation of overall fuel decay rates using the estimated radical concentrations shows good agreement with the measured 1-methylnaphthalene consumption for all of the experimentally investigated stoichiometries, giving convincing evidence for the validity of the proposed consumption routes. Computed fuel decay path fluxes reveal that under flow reactor conditions abstraction of a ＇＇benzylic＇＇ hydrogen from the methyl side chain dominates consumption of 1-methylnaphthalene, although O atom addition to the aromatic ring, displacement of the side chain by H atom, and homolytic decay also contribute significantly. Changes in the l-methylnaphthalene decay mechanism under higher temperature combustion environments and the oxidation mechanisms of even larger polycyclic aromatic hydrocarbons are postulated.