The rate constants for reaction of XO (X = Cl, Br, I) with dimethyl sulfide (DMS) have been computed at high levels of theory. Two reaction pathways were considered: (1) the oxygen-atom transfer (OAT) by XO (X = Cl, Br, I) to form X and dimethyl sulfoxide (DMSO) and (2) the abstraction of hydrogen by XO (X = Cl, Br, I) to form XOH and MeSCH2. Both reactions proceed via the formation of a very weak XO-DMS complex which can be described by natural bond orbital (NBO) analysis as a two-center one-electron (2c-1e) interaction where two alpha-spin electrons occupy lone pair orbitals (one localized on the oxygen atom and the other localized on the sulfur atom) and a beta-spin electron occupies a sigma bonding orbital (beta-bond). The calculated OAT reaction rates of ClO, BrO, and IO with DMS are 3.0 x 10(-15) cm(3.)s(-1), 8.7 x 10(-13) cm(3.)s(-1) and 1.5 x 10(-11) cm(3.)s(-1), respectively, at 298 K and 760 Torr. The abstraction pathway is less favored in the order ClO > BrO > IO with computed branching ratios (OAT/abstraction) of 2.7, 98, and 15000, for ClO, BrO, and IO, respectively.