Diffusion of carbon dioxide (CO2) in a carbonated water-oil system is of great importance for proper design of CO2-based enhanced oil recovery (EOR) processes. We study the effects of operational parameters such as saturation pressure, temperature, and phase volumes on diffusion coefficients of CO2 in a carbonated water-oil system. Results show that diffusion coefficients of CO2 in both phases are susceptible to saturation pressure. The greater the saturation pressure, the larger the diffusion coefficients. At a given saturation pressure, diffusion coefficients of CO2 in two phases increase by increasing temperature. Values of the coefficients determined at 40 degrees C are about twice those determined at 20 degrees C. The equilibration of the system was found to be much faster at the higher temperature. The results indicate that the predicted diffusion coefficients are insensitive to phase volumes, indicating applicability of the determined diffusion coefficients to simulate the mass transfer in large-scale reservoirs.