A four-dimensional intermolecular potential energy surface (PES) for two rigid carbon dioxide molecules was determined from quantum-chemical ab initio calculations. Interaction energies for 1229 CO₂-CO₂ configurations were computed at the CCSD(T) level of theory using basis sets up to aug-cc-pVQZ supple-mented with bond functions. An analytical site-site potential function with seven sites per CO₂ molecule was fitted to the interaction energies. The PES was validated by calculating the second virial coefficient as well as viscosity and thermal conductivity in the dilute-gas limit.