Hydrodesulfurization experiments have been carried out in a cocurrent down-flow trickle-bed reactor over two commercially available high activity Co-Mo/Al2O3 catalysts (A & B) using diesel oil as feed stock. Similar drying and presulfiding procedures are followed for both the catalysts. The efficiency of these catalysts is evaluated based on catalyst activity and compared at typical operating conditions. It is found that the catalyst-A exhibits higher activity than the catalyst-B.