The oil sands fine solids contain both organic and inorganic components. The former is typically toluene insoluble organic matter that possesses a high degree of hydrophobicity, while the latter is mostly fine clay minerals that are naturally hydrophilic. The organic components do not usually appear alone but are coated on the clay minerals surfaces rendering them partly hydrophobic and partly hydrophilic. Such highly heterogeneous clay minerals are conventionally described by an ill-defined term "biwettable". However, quantifying the bi-wettability of oil sands fine solids has proven to be challenging. In this paper, we have attempted to quantify the bi-wetting properties of the oil sands fine solids using a "bi-wetting index" calculated from a combination of film flotation and water vapor adsorption. A higher bi-wetting index corresponds to a higher degree of hydrophilicity. Three model fine solids (high purity kaolinite, bitumen treated kaolinite, and silane coupling agent modified kaolinite) and two oil sands fine solids samples were used. The results showed that bitumen and silane coupling agent modified kaolinite, with bi-wetting indexes of 0.11 mN.mol/m(3) and 0.18 mN.mol/m(3), respectively, were more hydrophobic than pure kaolinite with a bi-wetting index in excess of 0.28 mN.mol/m(3). The hydrophilicity/hydrophobicity of silane coupling agent modified kaolinite was between that of kaolinite alone and bitumen modified kaolinite. The fine solids and heat treated fine solids were clearly more hydrophilic than kaolinite with bi-wetting indexes >0.58 mN.mol/m(3) and >0.61 mN.mol/m(3), respectively. The fine solids were more hydrophobic than the heat treated fine solids. This first proposed bi-wetting index obtained from combined film flotation and water vapor adsorption methods appears to be an effective way to quantify the bi-wetting properties of fine solids isolated from the oil sands. (C) 2017 Elsevier Ltd. All rights reserved.