In natural gas processing, the presence of acid gases such as CO2 and H2S affect the gas treatment. Natural gas streams should have the content of such gases reduced to attain technical restrictions. In gas purification processes, phenomenological modelling requires the knowledge of thermophysical properties. Therefore, this work aimed to apply Peng-Robinson equation of state (PR-EoS) and van der Waals mixing rules (vdW-MR) to estimate density (ρ) and specific heat at constant pressure (CP) for methane, carbon dioxide, hydrogen sulfide, and a methane + carbon dioxide mixture at temperatures between 300 to 313.15 K, and pressures from 1 to 100 bar. Equations were implemented in MATLAB. Estimated ρ and CP values were compared with data available in literature. The results indicate that PR-EoS and vdW-MR can be used to predict such properties accurately.