Three regularities have been introduced for liqs. (T < TC and  > C) based on av. potential energy. The exptl. data have been used to show the validity of the regularities. First, there exists near-linearity relation between PiV4m and  for all isotherms of a liq., where Pi and  are internal pressure and d., resp. Second, (2Z - 1)V3m changes linearly with  for each isotherm of any liq., where Z and Vm are compressibility factor and molar volume, resp. Third, a new regularity using the definition of bulk modulus and the newly proposed equation of state between reduced bulk modulus and d. has been introduced, that is (Br - 0.5)V3m vs.  must be linear for all isotherms of a liq. where Br is the reduced bulk modulus. A new equation of state has been also derived. The d. of some liqs. in the extensive ranges of temp. and pressure has been calcd. using the new equation of state. The densities calcd. from this equation agree with expt. to better than 0.3 %. The new equation of state can predict internal pressure, thermal expansion coeff., and isothermal compressibility of liqs. within exptl. error.

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