Results of determination and analysis of the composition of bitumen-air aggregates floating to froth layer during processing two types of the oil sands: an average grade (11.1% bitumen Estuarine ore) and a low grade (7.2% bitumen Marine ore) are presented. Flux of the bitumen- air aggregates floating to the froth layer inside the Syncrude Research EXP Primary Separation Vessel was monitored and recorded on videotapes using the Luba Tube sampling technique. Sequences of the frames grabbed from these video recordings were analysed to determine the aggregate dimensions, shapes and rise velocities. On a basis of the aggregates' dimensions and rise velocities the composition of the aggregates was evaluated. Three reference state models were presented. In addition to the two models described in an earlier study, a new theoretical approximation (called model C) describing velocity of contaminated bubbles within a range of Reynolds numbers 0.2 < Re < 20000 was developed. The model C was found to be the most suitable choice as a “reference state” necessary for the aggregate composition calculation. It was found that the average aggregate size and the amount of the bitumen carried to the froth layer depended on the grade of the oil sand processed. In the case the average grade oil sand the average value of the Feret diameter was of an order of 1 mm and the average aggregate contained ca. 8.6*10^-4 g of bitumen. In the case of a low grade oil sand the average value of the Feret diameter was lower (0.6 mm) and the average aggregate contained less bitumen (ca. 1.3*10^-4 g).