In response to the First Industrial Fluid Simulation Challenge issued by the Computational Molecular Science and Engineering Forum (CoMSEF) of American Institute of Chemical Engineers (AlChE), we have performed osmotic molecular dynamics (OMD) simulations on model mixtures representing propylene + dimethyl ether and nitroethane + propylene glycol monomethyl ether (PGME) at each of two temperatures. The models are standard force-field models available in the literature for site-site interactions between heavy nuclei. Coulombic and Lennard-Jones (LJ) potentials are defined at each site and cross Lennard-Jones interactions are obtained from the Lorentz-Berthelot combining rules. OMD simulations yield the activity coefficients for each component in the mixture at the specified composition. However, because values of individual activity coefficients are less accurate for smaller mole fractions, when the composition difference across the membrane is large, we have chosen to impose thermodynamic consistency to smooth the data over the whole composition range. This is done by fitting simulated values of both activity coefficients simultaneously to the Wilson activity coefficient correlation. P-xy diagrams and data are then reported at the desired compositions for both systems at two different temperatures using the smoothed activity coefficients. (C) 2003 Elsevier B.V. All rights reserved.