Thermodynamic properties were calculated with various cubic equations of state for the model compounds of coal liquids and their mixtures. These properties included vapor pressure, molar volume, excess volume, excess enthalpy, and vapor-liquid equilibrium. Liquid densities were also measured in this work for bicyclohexyl and mixtures of quinoline + tetralin to complement the experimental data of importance to coal liquefaction processes. The Patel-Teja equation of state yielded better results for calculations of vapor pressures and liquid molar volumes. The values of binary interaction parameter k(a12) as determined from different types of mixture properties were compared and examined for their reliability. The results showed that excess volumes were capable of serving as a reliable data basis for determination of the binary interaction parameter.