The evaluation of thermophysical properties for dynamic simulations of chemical processes is often too time consuming for the real-time simulation of complex processes. This holds particularly for the calculation of phase equilibria. For them so-called local models were developed to determine equilibrium coefficients or relative volatilities. Such models contain parameters to be fitted to reliable phase equilibria in a certain area of the state space. When limits of applicability are exceeded or when the error is too big, the parameters must be actualized. In local models developed up to now, Porter’s equation for the activity coefficient is used. Usually the equilibrium coefficients of all components are related to that of the dominant component. The error of such models increases with the number of components in the mixture so that the models become unsuitable for multicomponent mixtures. In this work a local model for multicomponent mixtures is presented. The basic idea of this so-called "group model" is that mixtures can be classified into groups of substances with thermophysically similar behaviour. Each component in a mixture is attributed to one of these groups. Then group equilibrium coefficients taking into account the interactions between the groups, and equilibrium coefficients for all substances considering interactions within the groups, are evaluated. It is shown that this group model provides a sufficiently precise and efficient evaluation of equilibrium coefficients for multicomponent mixtures during dynamic simulation.