High-resolution sulfur 1s NEXAFS spectra of a series of sulfoxides and sulfones have been obtained, and are assigned with the aid of ab initio improved virtual orbital (IVO) calculations. Spectral differences between sulfones and sulfoxides are attributed to the sulfur oxidation state and the energy spacing between unoccupied molecular orbitals. The character of the white line in sulfones depends on the sulfur ligand groups, where an aromatic ligand causes a red shift and a broadening of the white line. These effects can pose challenges for speciation when the white line of sulfones overlaps with that of sulfoxide. (C) 2013 Elsevier B.V. All rights reserved.