The Spinco E analytical ultracentrifuge has been used to determine specific volumes or densities for organic liquids and water at pressure from 1 to 100 bars. Specific volumes calculated from experimental isothermal compressibilities (βT) were in very close agreement with values from measurements recorded in literature. Bulk modulus (1/βT) vs. pressure plots indicated that the Lennard–Jones 6-12 potential does not satisfactorily describe the molecular interactions for carbon tetrachloride, benzene, cyclohexane, or water. The organic liquids were reasonably approximated by a 7-28 potential or more exactly by a 6-24 potential. None of the two-term potentials could account for the interaction of water molecules.