Abstract: The Pulley System Powered by Loss of Buoyancy is a design to configure a buoyant vessel, a pulley, and a counter-weight such that they form a system that can produce a positive work output that can be used to drive gears. The core idea of this design is the use of loss of buoyancy as a power source. The Pulley System Powered by Loss of Buoyancy is a system that can drive gears using loss of buoyancy as the source of power. Industry standard aluminum alloy or carbon fiber composite materials can be used to construct the system. (Refer to FIG. 1.) Vessel A has a floor, 4 walls, and an open top. The vessel is constructed of aluminum alloy or carbon fiber composite material. The vessel is initially buoyant and is placed in a lake, reservoir, or tank with adequate water supply. Vessel A is attached to a counter-weight E via cable that runs through pulleys C and D. Vessel A is also attached via wheels K to rail track G. Electronically activated valves B open and cause Vessel A to be flooded with water.