Densities were measured for liquid mixtures of m-xylene + quinoline and m-xylene + tetralin (1,2,3,4-tetrahydronaphthalene) at temperatures from 333.15 K to 413.15 K and pressures up to 30 MPa. The Tait equation correlated accurately the results. Isothermal compressibilities of the fluids and their mixtures were calculated with the aid of the Tait equation. The excess volumes of m-xylene + quinoline and m-xylene + tetralin were found to be negative at the experimental conditions.