Athabasca bitumen vacuum bottom (ABVB) was fractionated into 66.9% maltenes (n-pentane-solubles), 32.2% asphaltenes (11-pentaneinsolubles). and 0.9% coke (toluene-insolubles). The maltenes were subsequently split into four sub-fractions: 5.6% saturates (MF1) 2.6% mono and diaromatics (MF2). 38.2% polyaromatics (MF3), and 20.3% polars (MF4). Yield maximization of the desirable light MF1 and MF2 sub-fractions was explored according to three catalytic (Mo) scenarios: (i) a one-step ABVB hydrocracking with light products recovery, (ii) two-step process consisting of ABVB hydrocracking followed by the hydrocracking of the maltenic MF3 + MF4 sub-fractions; and (iii) one-step ABVB hydrocracking with specific pretreatment procedures to enhance contacting between Mo-based catalyst and the heavy oil. The products yield distribution was mapped according to a severity parameter combining temperature and time. Coke and gas formation increased with increased severity while asphaltenes and total maltenes decreased. For scenario (i), the optimum severity factor for the highest light products yield was 7.2. At this severity the ensemble of saturates, plus mono and diaromatics reached 32.7%. For scenario (ii). the optimum severity factors were 6.9 and 7.0 for the first and second hydrocracking steps, respectively, resulting in a total light products yield of 45.4%.. In scenario (iii) where options such as increasing the catalyst concentration, removal of oil-borne coke before hydrocracking and ultrasonic mixing,. the maximum MF1 + MF2 yield reached 50.8% on raw ABVB weight basis at a severity factor of 7.2. (C) 2004 Elsevier Ltd. All rights reserved.