Excess thermodynamic quantities have been calculated from volumetric data for liquid mixtures of 1,2-dichloroethane (DCE) with 2,2,4-trimethylpentane (TMP) over the temperature range 278.15 to 338.15 K for pressures up to the lower of either near the freezing pressure of DCE or 280 MPa. There are indications that pressure- or temperature-induced variations in the relative proportions of the trans and gauche forms of DCE affect the excess properties of the mixtures.