The terminal rise velocities of 20- to 1000-μm-diameter air bubbles in water and seawater were measured at atmospheric pressure and room temperature. The velocities were the same in both liquids for bubbles with diameters less than 450 μm. Above 450 μm the rise velocities were higher in water than in seawater. For all diameters tested, the measured velocities fell between those expected for bubbles with ''frozen'' surfaces and those expected for bubbles with fluid surfaces which exhibit internal circulation. ¿American Geophysical Union 1991