Characterisation of complex mixtures is a common tool especially in oil processing industry. Characterisation procedures result in experimentally gained characterisation curves, but for the simulation of industrial processes the definition of a substitute mixture is required. Traditionally, a system of pseudocomponents is derived from the True Boiling Point (TBP) characterisation curve, but there are a number of disadvantages, e.g. the physical properties of pseudocomponents must be estimated by unreliable empirical methods. The new approach to the characterisation of complex mixtures is based on representing the original mixture by a system of real components. Such substitute mixture is fully defined, it has a chemical character, and physical properties can be simply retrieved from databases. Utilisation of a substitute mixture of real components in the simulation of crude oil processing proved that the new approach could replace the traditional one in normal boiling temperature ranges where real components are available. Both approaches could be also easily combined. (c) 2005 Elsevier Ltd. All rights reserved.