Analytical formulae, rather than tables of thermodynamic and physical properties of important engineering materials over different ranges of operating conditions, are desired for performance analysis of many industrial and research applications.Many equations of state, using different number of variables, have been suggested but the simplest are the two-constant equations of state, such as the Soave-Redlich-Kwong (SRK) and the Peng-Robinson (PR) equations. The two equations are used, in this work, to predict thermodynamic properties such as pressure, internal energy, enthalpy, and entropy for steam, R12 and ammonia in the superheated region, in addition to NH3-H2O solution.Results of detailed calculations using a specially devised computer program showed that the SRK and PR equations give relatively low errors over wide regions. This justifies their utility over empirical multiconstant complex equations, for engineering computations.