A comprehensive study was conducted to evaluate the contributions of sulfur dioxide (SO2) and oxygen (O-2) to the degradation of monoethanolamine (MEA) during CO2 capture from power-plant flue gas streams. The study was performed in a 600-mL semibatch autoclave reactor, using aqueous MEA concentrations in the range of 3-7 mol/L at temperatures in the range of 328-413 K and a constant gas pressure of 250 kPa. The aqueous MEA was contacted with SO2/O-2/N-2 gas mixtures that had SO2 concentrations in the range of 6-196 ppm and O-2 concentrations in the range of 6-100 mol %. The effects of CO2 and a corrosion inhibitor (NaVO3) were also evaluated. The results showed that both SO2 and O-2 were detrimental, because they accelerated the rate of MEA degradation. NaVO3 also accelerated the MEA degradation rate, whereas CO2 had the opposite effect. A new kinetic model was formulated to account for the presence of O-2 and the option of the presence or absence of SO2 in the flue gas stream. This was of the form: -r(MEA) = 0.00745exp(45258 / RT)[ MEA](1.9)[CO2](-0.3) {[SO2](3.4) + [O-2](2.8)}