Cosmo Oil has successfully developed a new CoMo HDS catalyst, C-606A, for production of ultra-low sulfur diesel fuels. This catalyst was prepared by an impregnation method using a solution containing Co, Mo, P, and citric acid on a HY-Al2O3. The resulting catalyst air-dried only without calcination. The HDS activity was measured with straight-run light gas oil feedstocks under industrial hydrotreating conditions. C-606A had a three times higher HDS activity compared with the conventional CoMoP/Al2O3 catalyst. Commercial operation with C-606A has successfully demonstrated high performance. This catalyst has superior activity, which enables < 10-ppm sulfur content in products in a commercial hydrotreater designed to produce 500-ppm sulfur diesel fuels. (c) 2005 Elsevier B.V. All fights reserved.