Major operations in producing shale oil by conventional methods are mining, shale preparation (crushing, grinding, and screening), and retorting. Each of these operations requires major capital investment and substantial operating costs. Of these costs, mining accounts for about 50 percent; shale preparation, 15 percent; and retorting, 35 percent. Oil-shale technology in the United States is still in relatively early stage of development, and technologic advances that will effect substantial savings in costs undoubtedly will be made as research continues and an industry develops.