The kinetics of the CH 3 + HO 2 bimolecular reaction and the thermal decomposition of CH 3 OOH are studied theoretically. Direct variable reaction coordinate transition state theory (VRC-TST), coupled with high level multireference electronic structure calculations, is used to compute capture rates for the CH 3 + HO 2 reaction and to characterize the transition state of the barrierless CH 3 O + OH product chan-nel. The CH 2 O + H 2 O product channel and the CH 3 + HO 2 ? CH 4 + O 2 reaction are treated using var-iational transition state theory and the harmonic oscillator and rigid rotor approximations. Pressure dependence and product branching in the bimolecular and decomposition reactions are modeled using master equation simulations. The predicted rate coefficients for the major products channels of the bimo-lecular reaction, CH 3 O + OH and CH 4 + O 2 , are found to be in excellent agreement with values obtained in two recent modeling studies. The present calculations are also used to obtain rate coefficients for the CH 3 O + OH association/decomposition reaction.