In carbon capture processes based on chemical absorption, the solution used for absorbing carbon dioxide plays a central role and must be carefully selected. It is expected to have the potential to capture large amounts of carbon dioxide on the one hand, and to be fully regenerated at the lowest energy price on the other hand. As a continuation of a study initiated by Coulier et al. some years ago, the present work focuses on the measurement and modeling of thermodynamic properties of aqueous solvents containing methylpiperidines (a class of amines), potentially usable in carbon capture processes and leading to liquid-liquid phase split in process conditions. To complete liquid-liquid equilibrium (LLE), excess enthalpy and excess heat capacity data previously measured by Coulier et al. for the N-methylpiperidine + water and 2-methylpiperidine + water systems, LLE data, and excess-enthalpy data were measured for the 3-methylpiperidine + water and 4-methylpiperidine + water systems. To model all these data, a nonrandom two-liquid type activity-coefficient model was identified among tens of models as the most reliable one. Owing to the complex nature of interactions governing this type of systems, no less than 10 binary interaction parameters were necessary to ensure qualitative and quantitative correlations of our experimental data.