The general problem of elimination of sand, cuttings, and gas from aqueous dispersions of clay, commonly used in the rotary method of drilling oil wells, with reclamation of the colloidal content of the drilling fluid, is considered. Various mechanical devices for this purpose are briefly described and available data compared with laboratory findings on the rates of settling of particles from clay drilling fluids after chemical treatment. The colloid physics underlying the efficiency of chemical treatment is discussed. Graphs are given showing the superiority of chemical treatment of drilling fluids as compared with mechanical methods for reclaiming spent fluids. Treatment by chemical reagents has the great advantage of requiring no new equipment or expensive installation, and individual wells may be treated economically. Certain recommendations are made for maximum efficiency of the chemical method for field practice.