The kinetics of vapor-phase cracking of bitumen-derived heavy gas oil and the quality of the resulting liquid products were investigated at temperatures of 600-700 degrees C. Light ends components were analyzed by gas chromatography. The quality of the liquid product was characterized using simulated distillation, elemental analysis, and C-13 nuclear magnetic resonance spectroscopy. Consistent with vapor-phase cracking, the coke yield was negligible at less than 2%. The yields of C-2-C-3 olefins were 2-16 wt %, while the yields of C-2-C-3 alkanes ranged from 0.2 to 1.0 wt %. The hydrogen content of the liquid product decreased significantly with conversion, corresponding to an increase of the aromatic carbon content. A kinetic model that considered cracking of alkyl groups from aromatic rings fitted the conversion yields and the chemical compositions. The apparent activation energy of the cracking of reactive alkyl groups was 215 +/- 20 kJ/mol.