Gas bubbles, when entrained in water or other liquid, can generate high sound pressures in the liquid. Significant sound pressures are associated only with volume pulsations of the bubble, whereas oscillations in the shape of the bubble do not result in appreciable sound. Calculations have been made of the sound pressures resulting from excitation of volume pulsations by the following mechanisms: by bubble formation, coalescence, or division; by the motion of a free stream of liquid containing entrained bubbles past an obstacle; and by the flow of liquid containing entrained bubbles through a pipe past a constriction. The calculation of the sound pressure generated by bubble formation has been verified by measurements with bubbles formed at a nozzle.