Accumulation of partial decomposition products during methanol electrocatalysis influences both the product distribution and kinetics of reaction. To quantify the catalytic activity of Pt(111) to methanol oxidation, we performed chronoamperometric experiments at 0.6 V-RHE for varying durations (0.03-300 s). Subsequently, the coverage of accumulated residue was evaluated from linear sweep voltammetry performed in methanol-free electrolyte. A. straightforward mass and charge balance allowed for calculation of the yields of partial and complete oxidation products. From these time-dependent data, we extract kinetic and mechanistic information. In the first 30 ms of reaction, only partial decomposition products form on the surface without significant CO2 production. In contrast, for reaction periods longer than 5 s, CO2 production is greatly favored over residue formation. Time-dependent methanol reaction data and complementary CO oxidation measurements at 0.6 VRHE show that a serial reaction path, involving adsorbed residue, is inadequate to explain;the observed rate of CO2 production. As an alternative, we propose a dual path mechanism for methanol electrocatalysis when CO is the most abundant species. We find that a parallel pathway, not involving adsorbed CO, is responsible for the majority (greater than 80%) of CO2 produced. We present quantitative kinetic information regarding the rates of residue accumulation and CO2 production; we also briefly discuss the over-all mechanistic implications of our results for methanol electrocatalysis on Pt(111).