The hydrolysis of carbonyl suflfide (COS), catalyzed by tertiary amines, was studied in a gas‐liquid reactor at ambient conditions. Rate constants determined in a batch reactor were similar to those determined in a continuous flow reactor. A Bronsted plot of the reaction data over the amine basicity range, 0 < pKB < 14, suggested that both amine basicity and steric factors determine catalytic behavior. The reaction data suggest a mechanism analogous to one used to explain the base catalyzed reaction of isocyanates with hydroxyl compounds. The mechanism would involve complexation of COS with amine followed by hydrolysis of the complex.