A novel surrogate model useful for designing CO2 absorption columns is provided to describe the vapour-liquid equilibrium of CO2 in a flue gas or biogas and aqueous monoethanolamine (MEA). The surrogate model is adjusted with experimental data and compared with dedicated software for electrolyte mixtures, i.e. OLI®. The assessment of CO2 partial pressure is conducted at different MEA concentrations, temperatures and loading of CO2/ MEA in the liquid phase. The OLI® model is in good agreement with the experimental data when MEA concentration is between 15 to 30 % wt, as well as for high MEA concentrations (between 45 and 60 % wt) at 60 °C. However, for temperatures above 80 °C, the model is in agreement with experimental data only when the load of CO2 in the liquid phase exceeds the range from 0.25 to 0.30 (usual industrial operating range is from 0.2 to 0.4). A point not addressed in experimental data in literature is the presence of MEA in the vapour phase, which overcomes the recommended values from health safety point of view at 100 °C. The presence of MEA in biogas could produce NOx. The influence of inert gas (CH4) on the equilibrium is considered to check the model suitability for biogas enrichment. The novel surrogate model provides a good regression of all the experimental data in the operating region and it is validated using Pareto diagrams.