Molecular dynamics simulations of Na+ Cl- ion pairs in acetonitrile-dimethyl sulfoxide mixtures have been performed as a function of salt concentration and the composition of mixtures. Temperature dependence of the potentials of mean force (PMFs) is studied to assess the enthalpy and entropy contributions to the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of salt and mixture compositions. (C) 2014 Elsevier B.V. All rights reserved.