Experiments were conducted to study the effect of calcium ion and montmorillonite clay on bitumen displacement by an aqueous phase on a glass surface. Upon exposure to an aqueous environment containing calcium ion and clays, a thin coating of bitumen on a glass surface displaced spontaneously in the inward radial direction. The initially circular bitumen disk took the shape of a spherical droplet. The dynamic and static contact angles of bitumen on the glass surface were estimated by measuring the contact radius of bitumen with time. The dynamic and static contact angles in the presence of calcium ion and clays are compared with the case when no calcium ion and clays are present. At pH 9, the static contact angle decreased significantly in the presence of calcium ion having a concentration higher than 25 ppm. For a given temperature and at a pH of 9, the initial dynamic angle variation with time was affected less by the presence of clays than with the case of calcium addition. There was no synergetic effect on the dynamic and static angles due to the presence of both calcium ion and clays. In the presence calcium and clays, the results would suggest a negative impact on bitumen liberation from sand grains in the industrial process of bitumen extraction from oil sands. In all cases, the contact angle is measured through the bitumen phase. (C) 2004 Elsevier Ltd. All rights reserved.