The use of ionic liquids for CO2 capture and natural gas sweetening is being object of intense research. Within the enormous group of existing ionic liquids, those based on conjugate bases of carboxylic acids seem to be particularly promising. This work addresses the study of the high pressure CO2 solubility (up to 80MPa) in two protic ionic liquids, N-methyl-2-hydroxyethylammonium formate and N-methyl-2-hydroxyethylammonium acetate, in a wide range of temperatures (293–353K). A thermodynamic model based on the Peng–Robinson equation of state with the Wong–Sandler mixing rule, using the NRTL model for the activity coefficients, was here adopted to describe and evaluate the thermodynamic consistency of the experimental data. Furthermore, the study of a ternary mixture of CO2+CH4+N-methyl-2-hydroxyethylammonium acetate was investigated showing a high selectivity from the IL towards these solutes.