A tool for deploying plug balls or frac balls in a borehole utilizing the hydrostatic pressure of fluid in the borehole is disclosed. The tool includes two connected cylinders, the first cylinder with a larger cross-sectional area than the second cylinder. The tool includes two connected pistons, the first piston disposed in sealing engagement within the first cylinder, the second piston disposed in sealing engagement within the second cylinder. The tool includes a ball-holding tube connected to the second cylinder. Application of force to the first piston by exposing the first cylinder to the hydrostatic head of the borehole fluid causes the second piston to move which in turn applies force to the balls in the ball-holding tube which deploys the balls into the borehole by ejecting them from the tube.