Dilute suspensions of coal particles having average diameters of 1 mu m have been prepared from coals from the Shanxi Province, the People＇s Republic of China, and from the UK. The suspensions were stable only in the presence of surfactant repellants. Measurements of zeta potentials showed suspensions stabilised by non-ionic and ionic surfactants to behave very differently. The effects of the concentrations of repellant and of electrolyte, of the rank and maceral group composition of the coal and of the pH of the medium are contrasted for suspensions stabilised by a polyether, by CTAB and by a lignosulphonic acid. The non-ionic, polyether repellant which formed monolayers on the coal surface, each molecule being bound at more than one site, probably to oxygen groups, readily stabilised the colloidal system by pushing the zeta shear plane away from the coal surface. Larger concentrations of the ionic repellants were needed to confer stability, which they did by the formation of complex charged species on the coal surface.