Monoethanolamine (MEA) is commonly used to capture CO2 from combustion gases. A simple, fast, and accurate Fourier transform infrared method, via attenuated total reflectance, was developed to determine the liquid phase equilibrium speciation in related CO2 -MEA-H2O systems. Data were collected in a batch reactor at 1 atm pressure, temperatures of 20, 25, and 30 degrees C, and CO2 loadings of 0-0.6 mol CO2 /mol MEA. The main advantage of the method is that only the carbamate (RNHCOO- ) spectral peak height and CO2 loading are required to obtain the concentration profiles of the most prominent species present at reaction equilibrium. The profiles obtained were in good agreement (rmsd similar to 10(-3)) with the published data from other spectroscopic and titrimetric techniques as well as the predictions of a widely accepted vapor-liquid equilibrium model. The method has the potential to be developed into an in situ method of analysis for real time data acquisition from CO2 sequestration systems using aqueous MEA solvents.