A simple acoustic method was used to investigate the ternary mixture CO₂ + C₂H₆ + CHF₃ and the corresponding binary sub-systems. Critical data obtained on the binary mixtures of CO₂ + CHF₃ were used for comparison with values given in the literature using the traditional methods. The acoustic results are in agreement with those obtained by the conventional methods, within the combined experimental errors. The binary critical line of C₂H₆ + CHF₃ was determined over the whole composition range showing that this system deviates from ideality since the critical line exhibits a large temperature and a pressure minimum. The ternary system CO₂ + C₂H₆ + CHF₃ was investigated by a “ quasibinary” approach. Two different ratios of CO₂ to CHF₃ with four mixtures each were investigated. The “quasibinary” lines also show a distinctive temperature minimum. The course of the whole ternary critical surface was extrapolated. The Peng–Robinson equation of state, with conventional mixing and combining rules, was used to correlate the binary and ternary experimental data.