Phase identification is an important aspect of flash calculations which can affect the phase and chemical equilibria. A new simultaneous approach for reactive mixtures, based on tau-method which relies on modification equation for mole fraction summation, is introduced in this paper. In the proposed methodology, phase identification and solution of governing equations can be performed simultaneously and effectively. In addition, prior knowledge of the number of phases in advance is not required. Present methodology has been verified with the help of case studies and results are discussed in the present paper. The results indicate that the present method gives us information about presence of reactive phases at equilibrium, their quantities and compositions simultaneously. The method is easy to implement and it may be used by several thermodynamic models. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.