Colloidal interactions between bitumen and fines, extracted directly from oil sand ores, were investigated with zeta potential distribution measurement and surface force measurement using an atomic force microscope (AFM). Fines from good processing ores exhibit a negligible attachment to bitumen surfaces, due to hydrophilic nature of the fines. Fines from poor processing ores exhibit a stronger attachment to bitumen surfaces by an attractive hydrophobic force between bitumen and fines, due to hydrophobic nature of the fines and the presence of high concentration divalent cations in the processing water.