A detailed experimental study was performed in a trickle-bed reactor using bitumen derived gas oil. The objective of this work was to compare the activity of NiMo/Al2O3 catalyst containing boron or phosphorus for the hydrotreating and mild hydrocracking of bitumen derived gas oil. Experiments were performed at the temperature and LHSV of 340-420 degrees C and 0.5-2 h(-1), respectively, using NiMo/Al2O3 catalysts containing 1.7 wt% boron or 2.7 wt% phosphorus. In the temperature range of 340-390 degrees C, higher nitrogen conversion was observed from boron containing catalyst than that from phosphorus containing catalyst whereas in the same temperature range, phosphorus containing catalyst gave higher relative removal of sulfur than boron containing catalyst. Phosphorus containing catalyst showed excellent hydrocracking and mild hydrocracking activities at all operating conditions. Higher naphtha yield and selectivity were obtained using phosphorus containing catalyst at all operating conditions. Maximum gasoline selectivity of similar to 45 wt% was obtained at the temperature, pressure, and LHSV of 400 degrees C, 9.4 MPa and 0.5 h(-1). respectively, using catalyst containing 2.7 wt% phosphorus. (c) 2005 Elsevier Ltd. All rights reserved.