Air bubbles from 50 to 400 μm diameter were produced from a fine capillary tip inserted through the top of a rotating tank of water. Bubble persistence on the surface was measured from the tank geometry and rotation rate, the minimum detectable time being 10−2 s. In distilled water, nearly all bubbles >200 μm diameter persisted <0.05 s, but smaller bubbles existed for several seconds or more. Opposite results were found in seawater. Bubbles less than about 80 μm diameter existed ≤10−2 s. For larger bubbles, the residence time increased with size, reaching about 0.3 s for bubble diameters of 300 μm. These results, plus other experiments, suggest that bubble collisions in seawater will produce coalescence if one of the bubbles is less than about 80 μm diameter.