The purpose of this work is to study the absorption of carbon dioxide (CO2) through the free surface of a stagnant layer of polyolester oil in a closed cell via the pressure decay method. The system pressure and local temperatures in the vapor and liquid phases were recorded as a function of time for system temperatures of 25, 40, 55, and 70 degrees C. The tests were carried out for two initial heights of the liquid layer of 37 and 74 mm, respectively. The mass of CO2 that entered the cell was measured for each test. The data were used to validate a transient mass diffusion model that accounts for the departure from the ideal behavior. The model uses the PC-SAFT equation of state and incorporates the following nonideal effects: (i) gas compressibility in the vapor, (ii) liquid phase swelling, (iii) concentration-dependent nonideal density behavior, (iv) nonideal phase equilibrium at the vapor-liquid interface, and (v) concentration-dependent mass diffusivity. Absorption rates were found to be strongly dependent on, and inversely proportional to, the system temperature. The absolute average errors of the absolute pressure prediction were lower than 4%. When the nonideal effects are ignored, the absolute average errors can be as large as 30%.