A high-pressure expansion apparatus, described previously, has been used to measure the densities of {xXe + (1 - x)C2H4} at x = (0.0278, 0.489, and 0.759). The results reported in this paper cover the homogeneous gas and the Liquid regions in the temperature range from 273 K up to near the critical point of the mixture and at pressures up to 6.5 MPa. The molar volume of the gas, at the dew point pressure, and of the liquid, at the bubble point pressure, were obtained by extrapolation. Using the gas phase results, the second and third virial coefficients of the mixtures were calculated at T = 273 K.