Electrophoretic mobilities of various clays and their mixtures were measured atseveral temperatures in solutions having different pH values and differentconcentrations of added electrolytes (NaCI and CaCI2). Similarmeasurements have been made on kaolinite suspended in both real and syntheticoil sands tailings water. Further electrophoretic measurements have been madeon oil sands tailings sludge solids suspended in "clean" solutions and inboth real and synthetic tailings water. Results of these measurementsand others that are cited are consistent with the view that the stability ofsuspensions of fine minerals (mostly clays) in oil sand tailings issubstantially due to the properties of mixed clay colloids and possibly also tointeractions of these clays with bituminous organic substances that are sotightly bound to the clays that they are not removed by "ordinary"chemical treatment.