A relatively simple procedure is described to calculate the coordinates, temperature (T-az), pressure (P-az), and composition (x(1az)), of an azeotrope (for either an isothermal or isobaric binary system at low pressure and with a single or double homogeneous azeotrope) from an expression for the liquid-phase excess molar Gibbs function (g(E)). General results are based on (partial derivative g(E)/partial derivative x(1))(az) = RTaz In[p(2)(*)(T-az)/p(1)(*)(T-az)], and P-az = (gamma(1)p(1)(*))(az) = (gamma P-2(2)*)(az') where R is the gas constant, p(*) is saturation vapour pressure, and gamma is liquid-phase activity coefficient. Specific results are given for the Redlich-Kister, van Laar, Wilson, and NRTL equations. Numerical examples are provided for both an isothermal and an isobaric system. The procedure provides a means to obtain azeotrope coordinates that are consistent with a g(E) expression obtained either from experimental data or from a model. It is applicable to polyazeotropy, whereas the criteria given previously are generally not applicable to polyazeotropy.