The kinetics of the reaction between carbon monoxide (CO) and aqueous diethanolamine (DEA) were studied. It was established that CO reacts with aqueous DEA solutions to form formate ions and formyl-diethanolamine (DEAF). A reaction mechanism for this system is proposed and a mathematical model is developed to estimate kinetic and solubility data from absorption experiments conducted in a batch autoclave reactor for 313 less than or equal to T less than or equal to 413 K, 800 less than or equal to p(CO) less than or equal to 1100 kPa and 5 less than or equal to C-DEA less than or equal to 50 wt%. To verify the mechanism, experiments were also done with 30 wt% MDEA and 30 wt% DEA plus 20 wt% DEAF solutions. The data are consistent with a mechanism by which DEAF is predominantly formed by direct insertion of CO into DEA. The data also confirm that DEAF formation via the DEA-formate reaction is relatively slow and reversible. Since the Henry's constant of CO in aqueous DEA solutions is one of the key unknown parameters in the reaction model, a novel Nitrogen-Analogy was developed. Values of Henry's constants thus obtained were found to be in fairly good agreement with those estimated directly from the reaction model.