The CO2 equilibrium partial pressure and liquid film mass transfer coefficient (k(g)') in (7, 9, 11, and 13) m monoethanolamine (MEA) and (2, 5, 8, and 12) m piperazine (PZ) were measured in a wetted wall column. Also examined was 7 m MEA/2 m PZ. Absorption and desorption experiments were performed at (40, 60, 80, and 100) degrees C over a range of CO2 loading. Amine concentration does not affect the CO2 partial pressure of PZ or MEA solutions as a function of CO2 loading with less than 0.45 mols CO2/mol alkalinity. Changes in amine concentration and temperature often do not affect the measured value of k(g)'. At higher temperature and CO2 loading in PZ, the diffusion of reactants and products limits CO2 transfer, and k(g)' is depressed. PZ (8 m) exhibits a 70 % greater CO2 capacity than 7 m MEA and a 50 % greater CO2 capacity than 11 m MEA. k(g)' decreases by a factor of 30 in aqueous MEA with 0.23 to 0.50 CO2 loading. k(g)' decreases by a factor of 20 in aqueous PZ with 0.21 to 0.41 CO2 loading. PZ is shown to absorb CO2 2 to 3 times faster than MEA.