In 2009, Parsafar and his coworkers a simple functional form for a general equation of state based on an effective near-neighbor interaction of an extended Lennard-Jones (12,6,3) type, Using arguments analogous to those of Parsafar and Mason (in deriving ) they obtained the equation of statewhich is called in this thesis (because it builds on earlier linear regularities, and which perform well for particular materials). Three constants, and g are functions of temperature, and in general, all three functions to contain contributions from both the internal and thermal pressures. It gives an excellent representation of isotherms for widely differing materials and over wide ranges of density. is not a linear regularity because it contains two density-dependent terms, but with just three temperature dependent parameters, it appears to work very well for fluids and solids of any type. will be particularly useful in cases where both and prove inadequate. is based on an effective near-neighbor pair potential of the type. This is more general than the and forms used i and , respectively. This introduces one additional temperature-dependent parameter into , giving three adjustable parameters in total. In this thesis, the accuracy of the prediction of the thermal pressure coefficients of fluids (monatomic and polyatomic fluids, refrigerants and ionic liquids) via EOS(III) is evaluated and checked with experimental data. A new easy-to-program expression for the calculation of the thermal pressure of various rare gases, linear molecules, polar molecules, hydrocarbons, and refrigerants over the whole range of densities and temperatures, was developed by Bamdad, with an average relative error better than 2 percent. In the absence of experimental data, the predicted thermal pressure coefficients were checked with thermal pressure correlation function. Although Bamdad correlation function can predicts very well this coefficient, but working with it requires the adjustable parameters of the correlation function, which is obtained only for 20 fluids. It was shown that can predict thermal pressure coefficients accurately and propose an easy way for the calculation of this important coefficient. It is also shown that can predict properly the common regularities of dense fluids. The known regularites predicted by are common bulk modulus point at which bulk modulus versus density of different isotherms of any fluid intersect at that single point, common compression point at which the compression factor against density of different isotherms of any dense fluid intersects at that single point and some other known regularities. The equation of state,, is also applied for the evaluation of predicted thermophysical properties of ionic liquids. Three of well known ionic liquids with precise p, v, T data, imidazolium-based ILs,, and were chosen for this evaluation. It was shown that the accuracy of this equation of state is not good as normal fluids and decreases with increasing of ionic character of ionic liquids.