The hydrodenitrogenation of oil sands-derived heavy gas oil has been conducted in a trickle bed reactor over a commercial Ni-Mo/Al2O3 catalyst in the temperature range of 365-415 degreesC, pressure in the range of 65-88 bar, liquid hourly space velocity in the range of 0.5-2 h(-1). The hydrogen/heavy gas oil ratio has been changed from 400 to 1000 mL/mL. The study was conducted to determine the effects of these variables on the relative rates of conversion of total, basic, and nonbasic nitrogen compounds. It was observed that rate of conversion of nonbasic nitrogen compounds was lower than that of basic nitrogen compounds under identical process conditions. The pressure and hydrogen/heavy gas oil ratio have a more significant effect on the conversion of nonbasic nitrogen compound as compared to their effect on the conversion of basic nitrogen compounds. The effect of excess hydrogen sulfide on the conversion of basic and nonbasic nitrogen compounds has also been studied by adding butanethiol in-the feed gas oil. An increase in the quantity of butanethiol decreases the conversion of both basic and nonbasic nitrogen compounds. It was also observed that in the region of higher space time (about 1.5-2 h), the,conversion of nonbasic nitrogen compound increased:at a sharp rate as compared to that of basic nitrogen compounds. This may be possibly due to the generation of more basic nitrogen compounds from the nonbasic ones. The kinetics of the conversion of nitrogen compounds has also been studied in the present work.