SK Corporation has developed a new process, SK HDS Pretreatment process that enables the refiners to produce economically ultra-low-sulfur-diesel of below 10 ppm. This technology is based on the adsorptive removal of nitrogen containing compounds (NCC) from the feedstock to conventional hydrodesulfurization (HDS) units. The NCC is known to interfere with the activity of HDS catalysts. In the SK HDS Pretreatment Process, the feedstock to the HDS unit is pretreated, and 90% or more of NCC in the feedstock is removed, resulting in higher desulfurization in a conventional HDS unit. It was found that the degree of improvement in HDS is proportional to the degree of NCC removal. SK HDS Pretreatment Process is a cost-effective method for refineries to choose for 10 ppm ULSD production.