The method of analysis of bubble-solids aggregates flow inside a flotation cell, beneath froth layer, is presented. Size, shape, rise velocity and number of the aggregates were determined using a device called the Luba tube. The experiments were carried out at 25^oC in a 5.2 m diameter separation vessel used in a 100 tones per hour field pilot plant for oilsands processing. It was found that bitumen was transported to the froth layer in the form of irregular particles attached to air bubbles. A wide range of the bitumen –air aggregate sizes (from 0.13 mm to 2.84 mm) was observed with an average Feret diameter, i.e. an equivalent circular diameter of 0.68±0.35 mm. Under steady state conditions the average aggregate rise velocity was 6.8±1.8 cm/s with velocities varying from 3.0 to 12.6 cm/s. Mass of bitumen contained in a bitumen–air aggregate was determined on the basis of the experimental values of the aggregate size and rise velocity and the relationships describing velocity of unloaded contaminated (Model A) and clean (Model B) bubbles. It was found that mass of bitumen contained in a bubble-bitumen aggregate was of an order from 10-6 to 10-4 g depending on the aggregate dimension and the model used. The evaluated equivalent diameters of bitumen particle and air bubble making-up a bitumen–air aggregate were of a similar magnitude within ca. 0.2-1.2 mm range.