This paper reports PVT measurements for five gravimetrically prepared mixtures of CO2 + Na-2 from 225 K to 450 K at pressures up to 70 MPa. These results have been determined using a continuously-weighed pycnometer A detailed error analysis indicates that the accuracy of the densities is better than +/-0.1%. Additional PVT data for CO2 + N-2 mixtures have been measured by Netherlandse Gasunie, Ruhrgas, and Gaz de France as reported by Jaeschke and Humphreys (1990).