For the development and design of the various processes in the chemical, oil and gas processing, pharmaceutical, food and environmental industry, reliable thermophysical properties and particular phase equilibrium data are required. Because of the cost-intensive and time consuming measurement of the required data for the synthesis of unit operations or whole plants, the process engineer depends on models which are able to predict the thermophysical properties of the investigated systems reliably. Equations of state in contrast to g(E)-models show the advantage, that they can be applied to supercritical compounds and that they can be used to calculate enthalpies, heat capacities, densities (e.g. excess volumes), entropies, etc. of the pure compounds and their mixtures. After the development of g(E)-mixing rules, the group contribution concept could be applied for equations of state. This leads to group contribution equations of state like LCVM, PSRK, etc. In the meantime these group contribution equations of state were further revised by using an improved equation of state and better mixing rules. At the same time all kind of thermodynamic data are used to fit the required reliable temperature dependent group interaction parameters simultaneously to all kind of phase equilibrium data (VLE, gamma(sigma), LLE, SLE of eutectic systems, gas solubilities, azeotropic data) and excess properties (h(E), c(p)(E)) stored in the Dortmund Data Bank. The result is the universal group contribution equation of state VTPR which was first published in 2001 by Ahlers and Gmehling. (C) 2010 Elsevier B.V. All rights reserved.