The cross second virial coefficient and the dilute gas shear viscosity, thermal conductivity, and binary diffusion coefficient have been calculated for (CH4 + CO2), (CH4 + H2S), and (H2S + CO2) mixtures in the temperature range from (150 to 1200) K. The cross second virial coefficient was obtained using the Mayer-sampling Monte Carlo approach, while the transport properties were evaluated by means of the classical trajectory method. State-of-the-art intermolecular potential energy surfaces for the like and unlike species interactions were employed in the calculations. All potential energy surfaces are based on highly accurate quantum-chemical ab initio calculations, with the potentials for the unlike interactions reported in this work and those for the like interactions taken from our previous studies of the pure gases. The computed transport property values are in good agreement with the few available experimental data, which are limited to (CH4 + CO2) mixtures close to room temperature. The lack of reliable data makes the values of the thermophysical properties calculated in this work currently the most accurate estimates for low-density (CH4 + CO2), (CH4 + H2S), and (H2S + CO2) mixtures. Tables of recommended values for all investigated thermophysical properties as a function of temperature and composition are provided.