A thermodynamic model for predicting phase behavior of mixtures of hydrocarbons, organo-oxygenated compounds and water is required for the development of a biorefinery process simulator. Moreover, the design of particular fuel/biofuel blends also requires the support of a thermodynamic model to predict the properties of the final products. These types of mixtures are highly non-ideal due to the presence of association and solvation effects. The GCA-EoS model has already proven to have excellent predictive capacity to represent the complex phase behavior of mixtures containing natural products and biofuels. In this work we extend GCA-EoS to represent the phase equilibria of mixtures of branched hydrocarbons with water and alcohols. It is a big challenge for the model to cover, with a single set of parameters, the wide range of operating conditions found in processing, transportation and storage of these fluid mixtures. (C) 2011 Elsevier B.V. All rights reserved.