A constant gas-liquid interface reactor was used to measure carbonyl sulfide (COS) absorption rates in alkanolamine aqueous solutions. Two alkanolamines were studied: a secondary alkanolamine, diethanolamine (DEA), and a tertiary alkanolamine, N-methyldiethanolamine (MDEA) in the temperature range 313-353 K and for alkanolamine mass fractions going from 0.05 to 0.50. The reactor used is Lewis type, modified with a nonrotating valve which shortens considerably the cell loading time. For COS absorption in DEA aqueous solutions, the limiting step of the reaction is the deprotonation of the zwitterion. The kinetics data for COS absorption into MDEA aqueous solutions is interpreted using the base-catalyzed mechanism for the hydrolysis of COS. The new kinetic data show that previously reported results concerning the COS absorption by MDEA aqueous solutions were overestimated.