An extension of the anisotropic united atoms model is proposed for thiols and sulfides. A complete derivation of the nonbonded parameters is performed with the aim of obtaining a transferable force field. The electrostatic part of the intermolecular potential is represented by a set of atomic charges. These charges are extracted from quantum chemical calculations thanks to a method developed recently. These charges are shown to depend very weakly on the conformation of the molecule. The repulsion−dispersion interactions are described by an anisotropic united atom Lennard-Jones potential: parameters for methyl and methylene groups are directly taken from a previous study on alkanes, whereas parameters for −S and −SH groups are fitted to experimental data. The resulting potential, which we will term OPPE (optimized potential model for phase equilibria), is tested against liquid properties at atmospheric pressure and vapor−liquid-phase equilibria of various sulfides and thiols to prove its transferability. ...