An analytical cell to perform liquid sulfidation (30 bar, H-2/gas oil/4% DMDS) of HDS catalysts in industrial conditions was developed. It enables the alternate recording of time-resolved Mo and Co K edges X-ray absorption spectra of bimetallic catalysts under high pressure (30 bar) and temperature (350 degrees C) during the same reaction. Thanks to this cell, unique information about the concomitant electronic and local order transformation occurring around Mo and Co upon liquid sulfidation of a CoMoP/Al2O3 HDS catalyst has been obtained and discussed together with the ones recorded on a similar catalyst sulfided under academic gas sulfidation (1 bar, 15% H2S/H-2). A special emphasis on the evolution of the concentration profiles upon both activations has been carried out. On one hand, in industrial liquid sulfidation, polymolybdate species are slowly transformed into depolymerised oxides between room temperature and 230 degrees C, itself transformed abruptly into an oxysulfide, and then into a MoSx species mainly between 230 and 280 degrees C and finally into MoS2. On the other hand, gas sulfidation skips the depolymerisation process because of the room temperature supply of H2S and proceeds under a stepwise slow transformation of oxide into oxysulfide, itself into MoS3 species and finally into MoS2. Cobalt species under gas sulfidation goes through a CoS2-like intermediate whereas in liquid sulfidation, it is a 4-fold coordinated Co oxide species. Irrespective to the activation route, mixture of Co9S8 and CoMoS is obtained at advanced sulfidation stage above 200 degrees C.