Abstract: A ballast apparatus comprising a thin-walled plastic tube containing an open-celled plastic foam or other wicking material which may be selectively impregnated with a liquid which evaporates in air at room temperature. The tube defines an aperture through which the liquid may evaporate, the diameter of the aperture and the density and molar heat of vaporization of the liquid being such that the weight of the liquid which evaporates over time balances the reduction in buoyancy as gas particles diffuse through the balloon over the same time period. A control slide permits the user to adjust the mount of the wicking material exposed to or through the aperture. The ballast apparatus has a widened blade section which may be easily gripped by the user, and includes a tethering opening for attaching a cord or ribbon. The ballast apparatus is secured to the interior or exterior surface of the neck of the balloon using a double-faced adhesive tape.