The clay present in bituminous sand as a natural constituent plays a key role in the hot water separation process. Some clay is necessary for satisfactory results; more than enough decreases the yield of oil. When bituminous sand is mixed and heated with water into a mortar-like pulp preparatory to separation, the clay present causes the oil to disperse into flecks lying unattached among the sand grains. These oil flecks vary in size and in the amount of clay associated with them. On flooding the pulp with hot water the oil flecks of low clay content float on the surface as froth. The flecks of higher clay content become dispersed in the water. Increase of clay in the bituminous sand causes increase in the proportion of oil, which disperses. When bituminous sand is removed from the deposit and is stored, a change of association between oil and clay, which is detrimental to the hot water separation process, tends to take place.