Pressure-volume-temperature-composition (PVTX) properties of gas mixtures are important to model and predict flow and compression performance in a range of industrial processes. It is time consuming and sometimes impractical to obtain these properties from experiments. Here, molecular dynamics (MD) simulations were conducted to compute the thermodynamic volumetric properties of pure H2, CH4, CO2, and binary mixtures of H2/CH4 and H2/CO2 at temperatures of 310.9–470 K, pressures up to 172 MPa. MD simulation results were used to develop five analytical equations explicit in pressure as a function of density or volume, temperature, and composition, for the pure gases and mixtures. Our simulated results matched very well with the predictions from the established GERG-2008 equation and data published by NIST. The simplified equations of state (EOS) developed in this work will be more computationally efficient than other EOS for mixed systems. This can be significant in reservoir simulations. •Develop analytical PVT/PρT models for supercritical pure H2, CH4, CO2.•Develop analytical PVTX/PρTX models for supercritical H2/CH4 and H2/CO2 mixtures.•The models developed by this work were validated by simulated and experimental data.•The models developed can be more computationally efficient than other models.