Based on the multisolid-wax precipitation assumption for petroleum mixtures, a monotonic equation is proposed for the calculation of liquid and multisolid equilibria. Owing to the fact that the number of precipitating species can be determined instantly at fixed temperature and pressure through a stability analysis, the computation is fast and reliable. Although the developed iteration procedure is focus to liquid mixtures it is shown that can be easily incorporate into existing vapor-liquid iteration procedures based on the Rachford-Rice equation to get a vapor-liquid-multisolid-(wax) flash calculations. Numerical experimentations are shown and even more the proposed iteration method is used in the construction of phase boundaries without any problem. (C) 2013 Elsevier B.V. All rights reserved.