Thermophysical properties of 2-pyrrolidone (PYR), N-methyl-2-pyrrolidone (NMP), and N-cyclohexyl-2-pyrrolidone (CHP) binary and ternary liquid mixtures with methanol are reported at 298.15 K and 0.1 MPa over the full composition range. Excess and mixing properties derived from the experimental ones were correlated using Redlich-Kister (RK) equation, for binary mixtures, and Cibulka (C) equation, for ternary ones. Density Functional Theory (DFT) was also used to analyze structural and energetic features of cyclic lactams in gas phase and methanol solution. Results show the formation of H-bonding and dipolar interactions between cyclic amides and methanol, although these are weakened when a third component is added to the binary mixture, thus decreasing remarkably the values of ternary properties in comparison with binary ones and leading to the weakening of the binary blends' intermolecular interactions.