Densities were measured for liquid mixtures of m-xylene + hexadecane and tetralin + hexadecane at temperatures from 333 K to 413 K and pressures up to 30 MPa. The Tait equation correlated accurately the density data. Isothermal compressibilities of hexadecane and the mixtures were then calculated with the aid of the Tait equation. The excess volumes of m-xylene + hexadecane are positive over the entire experimental conditions. The isothermal excess volumes of tetralin + hexadecane are negative at 333 K and 373 K but were found to vary from positive to negative with increasing tetralin mole fraction at 413 K.