Pressure-composition isotherms for binary mixtures of carbon dioxide (CO2) + N-vinyl caprolactam (NVCL) and carbon dioxide (CO2) + N-methyl caprolactam (NMCL) were measured using a variable volume view cell at temperature from (323.15 to 353.15) K and pressure up to about 21 MPa. Phase behavior of these binary experimental data were correlated with Peng-Robinson equation of state using a van der Waals one-fluid mixing rule including two adjustable parameters. Critical constants were estimated with the Joback method, and the acentric factor was estimated with the Lee-Kesler method.