What altitude do you need oxygen to fly a hot air balloon?

Hot air balloons typically do not require supplemental oxygen until altitudes of around 10,000 feet (3,048 meters). At this elevation, the air density decreases significantly, which can lead to reduced oxygen levels. Pilots may choose to fly higher, but they should be aware of the potential for hypoxia and the need for oxygen systems if exceeding this altitude. Safety regulations and personal comfort levels will also dictate altitude limits for balloon flights.