Used NiMo/alumina residue hydrodemetallization catalysts with bimodal pore size distribution have been prepared in batch and continuous flow reactors using a Safanyia atmospheric residue. The batch reactor provided used catalysts containing carbon deposits with almost no metal deposits (less than 200 ppm V and 4 to 15 wt% C), whereas the continuous flow reactor provided used catalysts containing both metal and carbon deposits (up to 1.3 wt% V and 11 to 14 wt% C). Used catalyst elemental analysis indicates that within experimental uncertainties the carbon deposits have a density of 1.15+/-0.2 g/cm(3) and contain sulfur, nitrogen, and hydrogen with different H/C ratio, the latter depending on both the experimental conditions and the amount of carbon. Characterization of the used catalysts by electron probe microanalysis, secondary ion mass spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and porosimetry show that V and C were well distributed in the catalyst grain in most of the samples and that carbon deposits are best described by three-dimensional patches of amorphous carbon (young coke) which generate pore size restrictions. Both carbon and vanadium have a deactivating effect on toluene hydrogenation, cyclohexane isomerization, and thiophene hydrodesulfurization performed on used catalysts under 6 MPa hydrogen pressure. However, a small amount of vanadium well dispersed inside the catalyst grain has been found to be more deactivating than a large amount of carbon.