The compression factors Z of (methane + nitrogen) of various compositions were measured using a direct method in the temperature range 308.15 K to 333.15 K and at pressures up to 12.0 MPa. Unlike-interaction second virial coefficients were calculated from the data and compared with previous experimental values and values predicted by the Tsonopoulos and GERG equations. Unlike-interaction third virial coefficients were also calculated and compared with estimates provided by both the GERG correlations and the method given by Orbey and Vera.