Measurements of the thermodynamic properties for a series of more environmentally-friendly refrigerant mixtures containing hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), and carbon dioxide (CO2) were conducted. These new property data help increase confidence in the design and simulation of refrigeration processes that use CO2 + HFO + HFC refrigerant mixtures. The HFCs of interest were R32, R125, and R134a and the HFO tested was R1234yf. The measurements collected were prioritised to fill gaps in the available literature data. Vapour-liquid equilibrium plus liquid-phase density and heat capacity data were collected for different binary mixtures containing HFCs, HFOs and CO2, with the liquid phase measurements spanning (223 to 323) K and (1 to 5) MPa. The measured data, as well as data from the literature, were then used to tune the mixture parameters in the models used by NIST's REFPROP 10 software package to improve the prediction of thermodynamic properties for these fluids. To test the predictive capabilities of the models tuned to the binary mixtures, thermodynamic property data were also measured for four ternary mixtures and a five-component mixture of HFCs, HFOs and CO2. The new models developed in this work significantly improved the root mean square deviations of the predicted properties for these multi-component mixtures: the most significant reductions were about a factor of two in density.