A discharge-flow apparatus was used to determine the branching ratio &agr; for the channel of the reaction of ClO with CH3O2 that leads to the formation of CH3O. The experiments were performed at 2 Torr pressure and at room temperature. CLO was the excess reactant and was measured mass spectrometrically; CH3O was detected by laser-induced fluorescence. The value of &agr; was shown to depend on the fraction &bgr; of the reaction of CH3O2 with Cl atoms that leads to the formation of CH3O. For &bgr;=0, 0.5 and 1, the derived values of &agr; are 0.28¿0.07, 0.32¿0.08 and 0.42¿0.09, respectively. Comparison with other published results suggests the possibility of three significant product channels for the reaction of CH3O2 with ClO. ¿ American Geophysical Union 1995