In this work, hydrotreating of heavy atmospheric gas oil, light vacuum gas oil, and heavy vacuum gas oil was carried out at pilot scale at the following operating conditions: reaction temperature of 340-380 degreesC, liquid hourly space velocity of 1.0-2.0 h(-1), pressure of 54 kg/cm(2), and a hydrogen-to-oil ratio of 2000 ft(3)/bbl. The hydrotreating of the three gas oils blended in a typical FCC feed volumetric ratio was also conducted at similar reaction conditions. From the experimental results it was confirmed that the mono-aromatics content exhibited an increase as the multi-ring compounds are saturated, which indicates that mono-aromatics are significantly more difficult to saturate. It was also observed that the quality of the final products obtained when the gas oils were hydrotreated separately is better than the typical FCC feed hydrotreating scheme. This behavior was attributed to the competition of the different reactions for active sites of the catalyst, which is higher when all the feeds are hydrotreated together due to the presence of sulfur and nitrogen in multi-ring aromatics type of structures in heavy feeds.