Abstract: Balloon altitude control is provided. A system includes a balloon formed from a material having latex. The balloon includes a top portion that is narrower than a middle portion of the balloon. The balloon includes a bottom portion that is in contact with a cable to tether the balloon to a gondola. The bottom portion of the balloon is narrower than the middle portion of the balloon. The system includes a first valve located at the top portion of the balloon. The first valve can open to release gas from within the balloon, and close to at least partially prevent the release of the gas from within the balloon. The system includes a gondola. The gondola includes a control system that can open the first valve to release the gas responsive to a determination to decrease buoyancy of the system.