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 forcefield. 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 repulsiondispersion 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. Excellent agreement is obtained with experimental data.