The solubility and absorption rate of carbon dioxide into monoethanolamine/piperazine/water were measured in a wetted wall column at 40-60degreesC. The total amine concentration was varied from 1.0 M to 5.0 M, with monoethanolamine blends containing 0 to 1.2 M piperazine. CO2 solubility and solution speciation were simulated by nine equilibrium reactions. Two of the equilibrium constants were adjusted to match literature data. The rate of absorption was predicted by the theory of diffusion with fast chemical reaction. Piperazine at 24 mol% of the total amine decreases CO2 equilibrium pressure by 50% and enhances the CO2 absorption rate by 50% to 100%. The CO2 enhancement factor decreases by a factor of 0.6 to 2 as loading decreases from 0 to 0.5 mol CO2/mole amine.