Oxygen levels on Mount Everest start to decrease significantly as climbers ascend to higher altitudes. At around 8,000 meters (26,246 feet) above sea level, the oxygen levels are only about one-third of those at sea level. This region, known as the "Death Zone," typically begins above the South Col (approximately 7,906 meters or 25,938 feet) on the Southeast Ridge route.
In the Death Zone, the lack of oxygen becomes a critical factor, making it extremely challenging for climbers to survive without supplemental oxygen. Most climbers rely on the use of bottled oxygen to maintain sufficient oxygen levels in their bodies and reduce the risk of altitude sickness, hypoxia, and other life-threatening conditions.
It's important to note that even with supplemental oxygen, climbing in the Death Zone is still highly demanding and dangerous due to the extreme cold, high winds, and harsh conditions. Only experienced mountaineers with proper training and support attempt to climb Mount Everest.