Vapor-liquid equilibria of binary and ternary mixtures containing nitrogen (N-2), oxygen (O-2), carbon dioxide (CO2) and ethane (C2H6) are studied by molecular simulation using two-center Lennard-Jones plus point quadrupole models. Pure-component models are taken from recent work. Mixtures are described using the Lorentz-Berthelot combining rules. Predictions of vapor-liquid equilibria from pure-component data alone agree well with experimental data, for example, the azeotropic behavior of the carbon dioxide + ethane system is predicted correctly. Further improvements are achieved by adjusting one parameter in the energetic term of the combining rule to binary data. For this purpose, a simple and efficient procedure is proposed. Excellent agreement between the molecular models and experimental data for vapor-liquid equilibria, saturated densities, and enthalpies of vaporization is observed for the five binary systems studied in the present work (N-2 + O-2, CO2 + C2H6, O-2 + CO2, N-2 + CO2, N-2 + C2H6). Vapor-liquid equilibria of two ternary mixtures (N-2 + O-2 + CO2, N-2 + CO2 + C2H6) are predicted well without any further adjustment of model parameters. Results from molecular simulation are compared to those from the Peng-Robinson equation of state, the PC-SAFT equation of state, and the BACKONE equation of state using the same data to determine model parameters. The quality of correlations with system-specific binary interaction parameters from molecular simulation and equations of state is similar, and the predictive power of molecular simulation is clearly superior.