The cross second virial coefficient and three dilute gas transport properties (shear viscosity, thermal conductivity, and binary diffusion coefficient) of mixtures of water (H₂O) and carbon dioxide (CO₂) were calculated with high accuracy for temperatures up to 2000 K using statistical thermodynamics and the kinetic theory of molecular gases, respectively. The required intermolecular potential energy surface (PES) for the H₂O–CO₂ interaction is presented in this work, while the like-species interactions were modeled using PESs from the literature. All three PESs are based on high-level quantum-chemical ab initio computations. The predicted values for the cross second virial coefficient are in satisfying agreement with the best experimental data. In the case of the transport properties, the calculated values should be more accurate than the few available data sets.