The reaction of a ground-state O atom with carbonyl sulfide is of interest for atmospheric (stratosphere and hot near-source volcanic plume) and combustion chemistry. In the present work, we employed a discharge-flow system combined with a modulated molecular beam mass spectrometry technique to measure the rate constant and products of the O + OCS reaction. The overall rate constant was determined either from the kinetics of the reaction product, SO radical, formation or under pseudo-first-order conditions from the decays of OCS in an excess of oxygen atoms: k1 = 1.92 × 10–12 × (T/298)2.08 exp(−1524/T) cm3 molecule–1 s–1 at T = 220–960 K, with conservative uncertainty of 20%. The yield of another reaction product, CO2, was found to increase from 3.55% at T = 455 K to 14.2% at T = 960 K, resulting in the following Arrhenius expression for the rate constant of the minor (S + CO2 forming) reaction channel: k1b = 4.19 × 10–11 exp(−4088/T) cm3 molecule–1 s–1 at T = 455–960 K (with an uncertainty of 25%). The kinetic and mechanistic data from the present work are discussed in comparison with previous experimental and computational studies.