Simulation and/or design as well as the control of operations in chemical engineering depend on an accurate knowledge of the behavior of matter under different, sometimes extreme, conditions of pressure and temperature. Numerous equations of state (EoS) are available in the literature, often assuming simplifications, such as the incompressibility of liquids to model their behaviour. In many practical applications, especially those involving high pressures, ignoring the effect of the coefficients of expansivity and/or compressibility of liquids leads to unforeseen errors. In this work, an EoS, F(ρ,T,p)=0, is obtained for pure substances in the liquid state region, which is checked for several data sets of different compounds. Once the model is defined, it is implemented in simulation/design calculations of process equipment and its influence on the calculations is evaluated. It is shown that the use of a suitable model justifies its use in vessel calculations.