We present a study of the phase diagram of a quadrupolar hard-sphere interaction site model of benzene using Monte Carlo simulation. Extensive calculations were made for the fluid phase and three solid phases for several values of the quadrupole moment. For an appropriate value of the quadrupole moment the model yields a volume change on freezing in good agreement with the experimental value for benzene. The results indicate that the relative stability of the high- and low-pressure solid phases of benzene can be understood qualitatively in terms of a competition between packing effects associated with short-range repulsions and electrostatic (quadrupole-quadrupole) interactions. A theoretical approach in which thermodynamic perturbation theory is used for the fluid phase and the cell theory for the solid phases gives a quite accurate description of the phase behavior in the model system. (C) 2001 American Institute of Physics.