Technical Abstract: The boundary coefficient of friction (COF) of FanteskTM starch-oil composite dry film lubricants was investigated as a function of starch chemistry (waxy vs. normal purified food grade corn starch), oil chemistry (hexadecane vs. oleic acid and various vegetable oils), and starch-to-oil ratio. Based on the results, a mechanism of starch-oil interaction in these composites was proposed. According to the proposed mechanism: a) the oil in the composite is distributed between the bulk and the surface of the starch, and b) the fraction of the oil trapped in the bulk and that adsorbed on the surface are related to each other by an equilibrium constant, and are functions of the total oil concentration in the composite. In line with the proposed mechanism, an adsorption model was used to quantify the free energy of adsorption ('Gads) of the polar oils onto the starch surface. The analysis gave 'Gads values that were higher than those reported for the adsorption of the same polar oils on steel surfaces. This result is consistent with the effect of the relative surface energies of steel and starch on the adsorption of polar oils. The adsorption property of the non-polar hexadecane, relative to the polar oils, was estimated by comparing their interfacial tensions with starch. The result showed a higher interfacial tension for hexadecane-starch than that for the polar oil-starch composites. This result predicts a relatively poorer compatibility, and hence, poorer adsorption of hexadecane on starch leading to higher COF, as was observed in the friction measurements.