In this study the kinetics of the aqueous-phase reaction between carbonyl sulfide and diethanolamine is investigated. Data were obtained in aqueous polyethylene glycol to test the nitrous oxide analogy method for estimating the physical solubility and diffusivity of carbonyl sulfide in aqueous amine solutions. The experimental data indicate that the nitrous oxide analogy method is applicable for carbonyl sulfide. The kinetics data are interpreted using the zwitterion mechanism. It is found that the limiting step in the reaction is the deprotonation of the zwitterion resulting in overall third-order kinetics.