A new equation of state was derived based on the nonrandom lattice fluid theory. By expanding the Helmholtz free energy from the full Guggenheim combinatory with vacant sites around the reference athermal solution, an approximate and explicit form was obtained. The model was tested for it’s applicability and parameters for 211 pure fluids were presented. It was found that the model describes quantitatively the P-rho-T property above critical. point, the saturated density, the vapor pressure, and the heat of vaporization of various molecularly complex fluids with only two temperature dependent molecular parameters for each pure fluid. The structure of the formalism for pure fluids can be readily extended to multicomponent mixtures.