Modelling, simulation and design of chemical processes need accurate and reliable estimation of the properties of the mixtures present in the process. In these situations, the property models are in a 'service' role where they supply the needed properties only when requested. Due to the solution procedures employed in simulation and design, the property models are required to have well-behaved and continuous derivatives for these problems to converge a solution. Furthermore, in process optimisation, the second and third order derivatives of the property models must exist for solution approaches based on mathematical programming. This paper describes the development of a computer aided system for the systematic derivation of appropriate property models to be used in the service role for a specified problem. As a first step, a library of well-known property models ha's been developed and a feature for parameter estimation has been added, so that for any selected model, the necessary model parameters can be estimated, fine-tuned and/or converted from one model to another model. Also, the property derivatives are validated and verified for thermodynamic and mathematical consistency.