A thermodynamic consistency (TC) test for the constant-temperature VLE data was investigated by numerically optimizing the binary parameters of the activity coefficient equations to satisfy the Gibbs-Duhem (GD) equation. It was shown that the one parameter Margules equation can best satisfy the GD equation, even if significant experimental errors are involved. A thermodynamic consistency (TC) criterion was defined using the one parameter Margules equation. The TC criterion showed that, of the 37 alkane-alkane, 18 methanol-water and 44 ethanol-water binaries, 36, 16 and 1 binaries are reliable, respectively. Simple liquid mixtures meet the TC criterion. (C) 2010 Elsevier B.V. All rights reserved.