Crude oil feedstock is becoming increasingly heavier with higher sulfur, conradson carbon residue (CCR) and asphaltenes contents. This trend will specifically impact residual oil processes aimed at converting the residual oil to distillate products and hydrotreating the residual oil to low sulfur fuel oils (LSFO). In this paper, the performance of a catalyst system typically used in industrial atmospheric residue desulfurization (ARDS) units was investigated using residual oils of Kuwait Export Crude (KEC) and Eocene Crude as feedstock. The catalyst system consists of a combination of five catalysts having different physico-chemical properties. The performance of the catalyst system was studied using a pilot plant equipped with two reactors in series for a complete life cycle. Sulfur content in the product for both tests was maintained at around 0.6%, by raising the temperature gradually to compensate for the catalyst deactivation. The tests were continued until the temperature of the back-end reactor (R2) reached 412 degrees C. The results showed that the life of the catalyst system using the atmospheric residues of KEC and Eocene was around 7500 and 3800 h, respectively. The results are discussed in terms of possible differences in the deactivation pattern caused by differences in the composition of the two types of crude oils used in the study. (C) 2007 Elsevier B.V.. All rights reserved.