Distillation assays provide the most widely used characterization data for modeling crude oils in refinery processes but can only define a relatively small fraction of the boiling curve for heavy oils. One way to extend the distillation range for heavy oils is to lower the distillation pressure while still avoiding thermal cracking temperatures. A vacuum distillation apparatus (DVFA-I) that was previously used to measure the vapor pressure of heavy components was modified to fractionate heavy oils and bitumens. The modified apparatus (DVFA-II) is a batch distillation system without reflux operating at pressures down to approximately 0.01 Pa, compared with 100 Pa for a conventional vacuum distillation. With the standard procedure developed for DVFA-II, up to 50 wt % of a Western Canadian bitumen was distilled into eight cuts plus a residue. This is an improvement over the 26 wt % distilled by a spinning band vacuum apparatus. The cumulative weight percent distilled was repeatable to within 2.3% for a given boiling point range. The densities and molecular weights of the cuts from two fractionations increased monotonically versus the weight percent distilled and were repeatable to within 0.18 and 4.0%, respectively.