Experiments have been done to reveal the entire process of clathrate hydrate formation on single bubbles of refrigerant vapor (CFC-11 or HCFC-141b) buoying up in a water medium. The hydrate appears on the surface of each bubble in the form of tiny particles, some of which are accumulated progressively on the surface, thus transforming the bubble into a solid hydrate balloon. The rest of them are spilled into the surrounding water. The heat balance on the bubble suggests that the convective discharge of the heat of hydrate formation into the water cannot be a controlling factor for the rate of hydrate formation.