Measurements of excess Xe + C2H4 are reported at eight temperatures between 205 and 273 K. In order to understand the different behavior of ethane when mixed with xenon, cross second virial coefficients, B-12, were theoretically calculated for both mixtures. Following the work of Kohler et al., this binary system Xe + C2H4, and the former one Xe + C2H6 were modeled as mixtures of spherical molecules (one-center Lennard-Jones, 1CLJ) with linear molecules (two-center Lennard-Jones, 2CLJ); the values of the unlike Lennard-Jones parameters, epsilon(12) and sigma(12), were varied so that the theoretical B-12 values would give the best fit of the experimental results. The results thus obtained in the gaseous mixtures are compared with previous studies in liquid mixtures.