This paper reports PVT measurements for five gravimetrically prepared CO2 + CH4 mixtures. A continuously-weighed, high-pressure pycnometer was used to measure densities at temperatures from 225 K to 350 K in 25 K increments and pressures to 35 MPa with one set of measurements to 69 MPa. A detailed error analysis indicates that the accuracy of the densities is better than +/-0.1%.