A pilot plant study was conducted to evaluate the effect of up to SO vol% light cycle oil (LCO) on product quality when it is used together with straight run gas oil (SRGO) as a hydrotreating feedstock. Experiments were carried out at reaction pressures of 54, 70 and 90 kg/cm(2); reaction temperatures of 350, 360, 370 and 380 degrees C, liquid hourly space velocity (LHSV) of 1.0, 1.5 and 2.0 h(-1), and constant hydrogen-to-oil ratio of 2000 ft(3)/bbl, over a commercial Co-Mo/gamma-Al2O3 catalyst. The experimental results were used to determine apparent reaction orders and activation energies, which agree with those reported in the literature.