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Molecular dynamics simulation and density functional theory were applied to calculate heats of immersion (Himm) of n-heptane, toluene, pyridine and water on two model sand surfaces and two model clay surfaces. Our results indicated that water showed the highest Himm for the model clay surfaces when multi-molecular water layers were used but the lowest when a single molecular layer was used. Simulations of a single molecular water layer sandwiched between a single molecular layer of the aforementioned organic compounds and the octahedral surface of clay indicated that the water layer was not stable. In particular, water molecules tended to desorb from the surface and clustered together to form water/water hydrogen bonds. Given the nature of bitumen molecules, the current results support the hypothesis that a pre-existing water layer on the sand and clay surfaces in raw oil sands is plausible so long as it is thick enough. / Chemical Engineering