The criteria for the stability of suspension concentrates, coal-oil mixture, are briefly described. The control of the stability of the suspension concentrates can be operated by the combination of three types of forces: (1) Electrostatic repulsion. (2) Steric repulsion. The origin of repulsion is from the adsorbed layers overlapping. (3) The van der Waals attraction between two spherical particles covered with a shell of a different material of thickness is given. A simple formula is obtained for stability ratio, which is not only applied to concentrated coal-oil mixture but also is applicable to dilute dispersions. The stability of the concentrated coal-oil mixtures depends on the maximum of the energy barriers, the volume fraction of particles, and the surface potential of the coal particle. Using the calculated results of stability ratio, the boundary lines between stable and unstable area of concentrated coal-oil mixtures at dissimilar volume fractions are obtained.