The Damkohler number (Da) is used to research the physical mechanisms leading to multiplicities and the effect of the hydrocarbon distribution on a light gasoil (LGO) deep hydrodesulfurization (HDS) two-bed catalytic distillation column. In doing so, three hydrocarbon mixtures are studied: a real LGO fraction, a synthetic gas oil mixture (SGO), and hexadecane (n-C-16). The parametric planes, Da(RR) and Da(B), were obtained for the three mixtures as a function of the reflux ratio, RR, and the bottom flow rate, B. The total sulfur regions (C-s) with respect to Da and RR, and Da and B, were also obtained. RR and B were chosen as bifurcation parameters, since they are frequently used for column operation. Results show that this system is controlled kinetically because the operating point and the multiplicity region lay on the kinetically controlled region (Da << 1). Results also show that the hydrocarbon distribution plays an important role in the occurrence of multiplicities, as well as exhibiting the importance of choosing a realistic gasoil fraction during process design and lab scale experiments. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.