Isobaric vapor-liquid equilibria (VLE) data for acetic acid + N-methyl pyrrolidone, acetic acid + N-methyl acetamide, water + acetic acid + N-methyl pyrrolidone, and water + acetic acid + N-methyl acetamide systems have been measured at 101.33 kPa using a recirculating still. The nonideality of the vapor phase caused by the association of the acetic acid has been corrected by the chemical theory and Hayden-O'Connell method. The experimental binary data have been correlated by the NRTL, UNIQUAC, and Wilson models. The three models with their best fitted binary parameters have been used to predict ternary VLE data. A comparison of three model performances was made by using the criterion of average absolute deviations in equilibrium temperature and vapor-phase composition. (c) 2006 Elsevier B.V. All rights reserved.