A liquid-liquid-solid separation procedure wherein a water-oil-coal-mineral matter slurry is allowed to come to equilibrium through mechanical agitation has for many years been applied to the separation of coal from mineral matter. The product is a black cottage cheese-like mass of agglomerated coal particles and oil suspended in the excess water which supports the dispersed mineral matter particles. A liquid bridge model which was proposed by earlier investigators is reviewed critically and used to estimate the free energy per unit area of the separation of coals of different ranks. Observations of the kinetics of the process suggest that the simple liquid bridge model is insufficient, probably due to the heterogeneous surfaces of the coal. An alternative model is proposed. 14 references.