Molecular simulation calculations are presented for two types of complex fluid mixtures, namely elastomer polymer mixtures and water-l-octanol binary and ternary mixtures. Elastomer polymers are used widely as membrane materials for gas separation. In this respect, the solubility and diffusion coefficient of gases need to be known accurately. Predictions for both properties are presented here. Water-1-octanol mixture is a widely used prototype system used to assess the partitioning of various chemical compounds with applications to chemical industry, biotechnology, etc. The microscopic structure of the water-1-octanol mixture is examined and the Gibbs free energy of solvation of four organic solutes is calculated. In all cases, detailed atomistic force fields are used to account for inter- and intra-molecular interactions. Simulation results are shown to be in excellent agreement with literature experimental data. (C) 2010 Elsevier B.V. All rights reserved.