Hydrodesulfurization (HDS) and Hydrodearomatization (HDA) of a real Straight Run Gas Oil (SRGO) were investigated over CoMo-S sulfide catalyst in a high-pressure fixed-bed integral reactor. The effect of the key process parameters on the quality of product was studied by varying the temperature (200-370oC), pressure (20 to 50 bar) and space velocity (1 to 4.7h-1). Experimental results revealed that HDS,% activity improved up to 81% when the temperature was increased up to 370oC but reduced to 60% with increase of space velocity up to 4.7 h-1. It has been also found that the rate of HDA, % activity enhanced up to 40.6% by increasing pressure up to 50 bar. The Cetane index underwent an increase of 1-3 degrees and gravity increased by 1-1.7 oAPI. The implication of these results on refining industry is that mild hydrotreating of diesel fuels using the single-stage technology will not enable local refineries to produce diesel fuel meeting the current specifications (<15 ppmwt) except with severe/deep once-through desulfurization or twostage once- through desulfurization with or without splitting the first reactor effluent.