In this study, the performance of three commercially available ARDS catalysts was investigated for the purpose of upgrading KEC-AR. The three catalysts chosen were based on NiMo/c-Al2O3 with varying NiMo loadings, porosities, and surface areas. KEC-AR was the 360 degrees C+ atmospheric derivative of Kuwait Export Crude (KEC). Testing was carried out using a fixed-bed reactor under operating conditions similar to the operating conditions applied on the actual ARDS units operated by Kuwait National Petroleum Company (KNPC). Catalyst performance testing was conducted at three reaction temperatures: 370, 390, and 410 degrees C. The results showed that vanadium removal from KEC-AR is highly dependent on the catalyst porosity; the wider and larger the catalyst pores were, the higher the vanadium conversion was. Additionally, it was observed that vanadium removal correlates proportionally with asphaltene conversion. Unlike vanadium removal, nickel removal showed a slight dependence on the NiMo loading. However, it did not show a clear dependence on asphaltene removal even though 70% of the nickel in KEC-AR is housed in the asphaltene fraction. Sulfur removal from KEC-AR was found to be dependent on two factors: the catalyst porosity and the catalytic sites. This was evident because it was observed that the catalyst that had intermediate properties in terms of porosity and NiMo loading was the most active among the others tested in this study. Asphaltene removal from KEC-AR showed clear dependence on the catalyst porosity; it was found that the catalyst with wider and larger pores was the most active among the others even though, quantitatively, the catalyst had the least NiMo loading and the smallest surface area when compared to the other two catalysts in this study. (C) 2015 Elsevier Ltd. All rights reserved.