Equilibrium interfacial tension (IFT) between toluene-diluted bitumen and a series of alkyltrimethylammonium bromide surfactant solutions was measured at various temperatures as a function of the carbon chain length of surfactants. A mixing and separating protocol to pre-equilibrate the aqueous and organic phases was introduced prior to the measurements. The influence of the equilibrated phase densities on the IFT values obtained by the pendant drop method is discussed. A possible systematic error in the assessment of the IFT values with the pendant drop and spinning drop methodologies was pointed out. In general, bitumen-aqueous phase IFTs increase with an increase in the temperature and decrease with an increase in the carbon chain length of the surfactants. During the equilibration process of the bitumen and aqueous phases, the phase densities change significantly, which has implications on the gravity drainage process.