Climbing Mount Everest without supplemental oxygen is an elite feat achieved by only a tiny fraction of total summiters—roughly 2% of all successful climbs. As of early 2026, the total number of individuals who have reached the peak "without O2" stands at approximately 225 to 235 people. The first to prove it was even physiologically possible were Reinhold Messner and Peter Habeler in 1978. Since then, the list has grown slowly due to the extreme risk of cerebral and pulmonary edema in the "Death Zone" above 8,000 meters, where the oxygen level is only a third of that at sea level. Most of these successful climbers are professional mountaineers or high-altitude Sherpas. It remains one of the most dangerous pursuits in sport; for every few people who succeed without oxygen, others have perished attempting the same feat. The vast majority of the 11,000+ total summits on Everest have relied on bottled oxygen to mitigate the debilitating effects of extreme altitude.