The kinetics of the reaction CH3 + 0 2 (+M) -+ CH302 (+MI have been studied, using the technique of flash photolysis and kinetic spectroscopy to follow the methyl radical concentration. The order of the reaction lies between 2 and 3 throughout the range of pressure from 25 to 380 torr at 22"C, and the results are consistent with a single reaction sequence:The limiting values of the third-order rate coefficients at low pressures are (3.6 f 0.3) X 10" 1. mole-2 sec-' when M is neopentane, and (0.94 f 0.03) X 10" L 2 mole-2 sec-' when M is nitrogen. The limiting value of the second-order rate coefficient at high pressures is (3.1 f 0.3) X lo8 1. mole-' sec-I. The rate constant for the independent second-order reaction CH3 + 0 2 -+ CH20 + OH is shown to be not much greater than 2 X lo5 1. mole-' sec-I, so that this reaction does not complete significantly with the combination reaction.This new interpretation is contrary to currently accepted views.