The excess molar enthalpies H-m(E) of [xCO(2) + (1 - x){C4H6O3 (propylene carbonate) or C7H13NO (N-methyl-epsilon-caprolactam) or C6H11NO (1-formyl piperidine)}] were measured at the temperatures 298.15 K and 308.15 K and pressures (7.5, 10.0, and 12.5) MPa. (Vapour + liquid) phase boundaries were determined from the H(m)(E)s. The excess enthalpies for all of the mixtures are negative over the entire composition, temperature, and pressure range. Large changes in the values of H-m(E) were observed near the critical temperature and pressure of carbon dioxide. The Peng-Robinson equation of state with a composition-dependent interaction parameter was used to model the behaviour of H-m(E). At low x the Peng-Robinson equation provided a satisfactory fit for all mixtures studied over the full range of pressures and temperatures. For {xCO(2) + (1 - x)C4H6O3}, the predicted H-m(E) values for x > 0.5 were more negative than the experimental results. The fits to the other mixing curves were somewhat better, but show similar discrepancies at T = 308.15 K and p = 7.5 MPa.