Oil sand ores mined at different locations in Alberta have different physical and chemical properties that dictate their processability by water-based bitumen extraction technology. In this study, the processability of one good processing ore and three poor processing ores has been investigated using a Denver flotation cell. The floatability of oil sand ores was found to vary significantly among the examined oil sand ores. Surface forces between bitumen-silica and bitumen-fines were measured using an atomic force microscope (AFM) to examine the mechanism of varying processability of oil sand ores. Factors examined include bitumen grade, fines content, divalent cation concentration, and weathering/aging. The results indicate that the processability of the ores cannot be simply evaluated from bitumen and fines content alone. Fines, divalent cations, and weathering/aging can significantly affect the processability of oil sand ores, either individually or collectively.