An oxidic Go-Mo catalyst presulfided by the SULFICAT(R) process has been studied by XPS. Results indicate that the strong interaction of the alkylpolysulfide with the solid provokes a partial reduction of both the sulfur and molybdenum ions. Treated under hydrogen, the adsorbed species decompose at temperatures as low as 150-220 degrees C converting the initial Mo6+ species into sulfided Mo4+. The sulfidation state of the active phase increases with the hydrogen pressure. Comparison with the conventional sulfiding procedure indicates that the SULFICAT(R) process results in a higher dispersion of the sulfided active phase.