Volumetric and second-derivative thermodynamic properties of binary mixtures of carbon dioxide and methane were calculated under supercritical conditions at pressures up to 99.93 MPa and temperatures between (323.15 and 573.15) K using molecular dynamics simulations with the multistate Bennett acceptance ratio technique. Eleven compositions were studied, ranging from pure methane to pure carbon dioxide in 0.10 increments in carbon dioxide mole fraction. The molecular simulations utilized the TraPPE and SAFT-? force fields to model methane and carbon dioxide. Because of the unavailability of experimental data, the results were compared against the extended range estimation and extrapolation of the GERG-2008 equation for the calculation of volume expansivity, isothermal compressibility, isobaric and isochoric heat capacities, JouleThomson coefficient, and speed of sound of the binary mixtures. The agreement between the simulation results and those obtained through the extrapolation of the GERG-2008 equation beyond its stated range of validity is quite good, suggesting that the force field representation of the binary mixture is accurate, especially when compared with the extrapolation of traditional cubic equations of state. Although more computationally expensive, molecular simulations relying upon only a few physically meaningful parameters are able to give similar results to those obtained with the semiempirical multiparameter GERG-2008 model.