Formulation optimisation is one of the more important steps in the development of surface coating systems. Several commercially available computer software packages that can be used to assist the formulation optimisation have been developed, provided that sufficient data are available. For systems having complex behaviour, more flexible techniques are needed. The approach that forms the basis of this paper is based on spline interpolations. Thus, the more complex behaviour of coating systems can be simulated and interpreted. The efficiency and the reliability of the models that have been developed have been evaluated using data that are relevant to anticorrosion coating systems. (C) 2003 Kluwer Academic Publishers.