Sulfided NiW and CoW catalysts supported on activated carbon and alumina were characterized with 57Co Mössbauer emission spectroscopy (MES) and EXAFS at the W–LIII edge. NiW catalysts were studied with MES by probing the Ni atoms with 57Co. MES results demonstrate that the Ni–W–S phase is present in sulfided NiW catalysts. Formation of Co9S8-type phases could be related to the lower thiophene HDS activity of CoW catalysts. W EXAFS showed that addition of Co or Ni to a W/Al2O3 catalyst results in a higher W sulfidation degree. No structural differences were found for carbon- and alumina-supported catalysts, in spite of the two times larger thiophene HDS activity of carbon-supported NiW.