Bitumen recovery from oil sands was found to severely deteriorate at operating temperatures lower than a "critical" value, suggesting a substantial change in one or more key process variables. A sharp increase in bitumen viscosity at lower temperatures has been considered as the major contributor to such deterioration. On the basis of the fact that the addition of selected chemicals does improve bitumen recovery without affecting bitumen viscosity, there must be other physicochemical factors that affect bitumen recovery and undergo a sharp change with temperature. In the present study, the interaction and adhesion forces between bitumen and sand grains or clays in water were measured as a function of temperature using an atomic force microscope. The results show that the measured adhesion force between clay and bitumen decreases with increasing temperature until a critical value of about 32-35 degrees C, above which the adhesion force disappears. As the adhesion force between clay and bitumen controls clay slime coating on bitumen surface and subsequently bitumen aeration, increase in the adhesion force with decreasing processing temperature would lead to slime coating and lower bitumen recovery. The effect of a chemical additive, methylisobutyl. carbinol (MIBC), on the colloidal forces was also studied. The results show that MIBC addition can reduce the adhesion force between clay and bitumen, thus facilitating bitumen aeration.