The production of hydroelectric power by pressure-retarded osmosis (PRO) at Great Salt Lake (GSL) maybe feasible with spiral module membranes receiving river water which would permeate into pressurized 12% brine from the southern half of the lake. The energy cost will depend largely on the attainment of adequate permeate flux through the membranes. In this regard the chief obstacle is the resistance to solute diffusion in the porous substructure of the membranes. If this resistance can be adequately reduced, a Jordan River PRO plant could produce 66 megawatts at a capital cost of 9,000 $ per kW and an energy cost of 0.09 $ per kWh. Similar results could be expected from a twin plant using the Weber River as the dilute solution, thus giving a total power output of about 130 megawatts. A third plant using the Bear River, together with 28% brine from the northern half of GSLm. is also possible and might give even better results because of the higher salinity of the north end brine.