The methoxy radical is an intermediate in the atmospheric oxidation of methane, and the branching ratio (k(1a)/k(1b)) (CH2DO center dot + O-2 -> CHDO + HO2 (1a) and CH2DO center dot + O-2 -> CH2O + DO2 (1b)) strongly influences the HD/H-2 ratio in the atmosphere, which is widely used to investigate the global cycling of molecular hydrogen. By using the FT-IR smog chamber technique, we measured the yields of CH2O and CHDO from the reaction at 250-333 K. Kinetic modeling was used to confirm the suppression of secondary chemistry. The resulting branching ratios are well fit by an Arrhenius expression: In(k(1a)/k(1b)) = (416 +/- 152)/T + (0.52 +/- 0.53), which agrees with the room-temperature results reported in the only previous study. The present results will be used to test our theoretical understanding of the role of tunneling in the methoxy + O-2 reaction, which is the prototype for the entire class of alkoxy + O-2 reactions.