Isochoric measurements were taken for the R23 + CO2 system for both the two-phase and the superheated vapor regions. The isochoric experiment covered a temperature range from 253 to 353 K and a pressure range from 1590 to 5880 kPa. The data in the two-phase region enabled VLE parameters to be derived using a flash method with the Carnahan-Starling-De Santis equation of state (EoS); in addition, the dew point for each isochore was found from the intersection of P-T sequences. The two derived parameters were compared with each other and a good consistency was found. The VLE data for the R23 + CO2 system were compared with results in the literature and a fair degree of agreement was found. The measured system showed positive deviation from Raoult's law that increases with rising of temperature. The P-V-T-x data in the superheated region were compared with the REFPROP 6.01 estimate for a wider temperature range than was previously measured by the Burnett method. The values predicted by the REFPROP 6.01 software show a positive deviation of about 0.4% in the comparison with the experimental data. (C) 2003 Elsevier B.V. All rights reserved.