Reliable data for the solubility of carbon dioxide in aqueous solutions of monoethanolamine are required for the design and evaluation of postcombustion carbon capture processes. As published experimental data for the solubility of carbon dioxide in aqueous solutions of monoethanolamine show considerable scatter, the solubility of carbon dioxide in aqueous solutions containing (15 and 30) mass percent of monoethanolamine; that is, (2.9 and 7.0) mol.(kg H2O)(-1) respectively, was measured at molar ratios of carbon dioxide to monoethanolamine in the liquid solution from 0.1 to 1.3 at (313, 353 and 393) K. An apparatus based on headspace gas chromatography (on the synthetic gas solubility method) was used for the experiments at low (high) gas loadings, that is, at partial pressures of carbon dioxide from (1 to 80) kPa (from (0.4 to 8.6) MPa). The new experimental results are compared to literature data and used to parametrize a physicochemical thermodynamic model based on the extended Pitzer equation for the Gibbs excess energy of the liquid mixture. Furthermore, model predictions for the ion speciation in the liquid phase are compared to literature data from NMR spectroscopy.