Weak nonbonded interactions between a divalent sulfur and an oxygen atom have attracted growing interest because of their roles in determining the structure and the biological activity of some organic sulfur compounds and in stabilising the folded protein structures. A survey of the Cambridge Structural Database (CSD) revealed hundreds of structures containing close intramolecular S...O contacts at distances shorter than the sum of the S and O van der Waals radii. Nevertheless, a close intramolecular contact in the solid state may result from either an attractive intramolecular interaction or from external forces imposed by crystal packing. This fact motivates the present study on two model systems for S¿O interactions in the liquid state, where the packing is not constraining the contacts: thiophene in furan and dimethyl sulfide in acetone.