Enhanced oil recovery by nitrogen injection is a tertiary oil recovery method that is actually used in certain Mexican fields. In order to describe or predict the process of nitrogen flooding by reservoir simulation, the phase behavior of nitrogen-oil systems has to be known. In this work. the perturbed-chain SAFT (PC-SAFT) equation of state was applied to the calculation of the vapor-liquid equilibria of nitrogen-hydrocarbon systems by using conventional one-fluid mixing rules. The binary interaction parameters, introduced in this equation to correct the segment-segment interactions of unlike chains, were estimated by minimizing the sum of squared relative deviations of bubble point pressures and the sum of squared deviations in mole fraction of phase equilibrium compositions. The calculation of the phase equilibria was carried out by minimization of the Gibbs free energy using stability tests to find the most stable state of the system. On the whole, the results show that the quality of the fit with the experimental data is good for most systems studied. Satisfactory predictions of the vapor-liquid equilibria of nitrogen-containing ternary and quaternary systems were obtained by using a generalized N-2-n-alkane binary interaction parameter for normal paraffins between methane and n-hexatriacontane. (C) 2003 Elsevier B.V. All rights reserved.