The modeling of an industrial trickle bed reactor (TBR) for hydrotreating (HDT) of vacuum gas oils (VGO) and other heavy fractions oils was developed based on experiments carried out under typical industrial conditions at pilot plant. Simultaneous reactions for hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodearomatization (HDA) and inhibition effects among different molecules such as decahydro-naphtalene, naphthalene, anthracene (mono-, di-, tri-aromatic), carbazole (non-basic nitrogen), acridine (basic nitrogen), dibenzotiophene (sulfur), and water, mixed with a vacuum gas oil severely hydrotreated (matrix feed), were taken into account. Analytical techniques selected for this research were nuclear magnetic resonance (NMR), for aromatic content and other analysis, ultra violet-visible spectrometry (UV-vis), for aromatic families, simulated distillation (SimDis), and standard tests (ASTM) to determinate basic nitrogen, total nitrogen, total sulfur, and other physicochemical properties of vacuum gas oils. (c) 2007 Elsevier B.V. All rights reserved.