The reactions of oxygen atoms with methyl, ethyl, and vinyl radicals are studied with a combination of ab initio quantum chemistry, variational transition state theory, and classical trajectory simulations. The interaction between the two radicals is examined with multi-reference configuration-interaction calculations employing augmented double zeta and augmented triple zeta basis sets. The implementation of analytic representations of the ab initio data within variable-reaction-coordinate (VRC) transition state theory (TST) yields predictions for the high-pressure limit addition rate coefficients. The dynamically corrected theoretical predictions for the CH 3 +O, C 2 H 5 +O, and C 2 H 3 +O high-pressure rate coefficients are well reproduced by the expressions 9.20×10 −11 T 0.050 exp(136/RT), 5.26×10 −11 T 0.032 exp(394/RT), and 1.71×10 −11 T 0.205 exp(427/RT)cm 3 molecule −1 s −1 , respectively, where R=1.987calmol −1 K −1 , for temperatures between 200 and 2500K. For the CH 3 +O reaction, these predictions are in remarkably good agreement with the extensive experimental data, while for the C 2 H 5 +O and C 2 H 3 +O reactions the theoretical predictions appear somewhat lower and higher, respectively, than the rather limited experimental data. VRC-TST analyses also suggest that the abstraction reactions to produce C 2 H 4 +OH and C 2 H 2 +OH have rate coefficients that are about 10% of the corresponding addition rate. Notably, the latter predictions have a significantly greater uncertainty, probably about a factor of 2, than do those for the addition. For comparison, the abstraction was experimentally observed to be about 21±8% of the total for C 2 H 5 +O, but was not observed in C 2 H 3 +O.