Two series of unsupported Co-Re and Ni-Re binary sulfide catalysts with variable atomic ratio alpha = Me/(Me + Re) from 0 to I were prepared by the co-maceration method. The catalysts were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and evaluated in the simultaneous hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions of a real gas oil feed under industrial relevant conditions. The results showed a synergetic effect of the Co or Ni sulfide on the ReS2 in both HDS and HDN reactions. A maximum in activity at the same atomic ratio alpha similar to 0.5 was observed for both reactions and both Co-Re and Ni-Re catalysts. The magnitude of the synergy was generally superior for HDS than for HDN, and at low reaction temperature (598 K) larger for Ni-Re than for Co-Re catalysts, especially in HDS, while at high temperature (648 K) it was reverse. Moreover, the Co-Re catalysts exhibited higher HDN/HDS selectivity than the Ni-Re catalysts. Neither XRD nor XPS results evidenced the presence of a "Co-Re-S" or "Ni-Re-S" like phase. It is suggested that the synergism could be associated to the hydrogen activation and spillover from the Co or Ni sulfide to ReS2 (c) 2005 Published by Elsevier B.V.