New experimental data are presented for the vapor-liquid equilibria in the binary systems nitrogen + methane, nitrogen + ethane, and methane + ethane including data for the saturated liquid densities covering a temperature range of 130 K to 270 K and pressures up to 10.1 MPa. On the basis of the new experimental data for these binary mixtures, which may be regarded as model mixtures, the performance of the widely used group contribution equations of state VTPR and PSRK was investigated. These studies focused on the equations' ability to represent accurately saturated liquid densities over a wide range of temperatures and pressures when a constant volume translation was applied.