Reinhold Messner and Peter Habeler first climbed Mount Everest without supplemental oxygen in 1978.
The Austrian climbers reached the summit on 8 May 1978, using the Southeast Ridge route from Nepal. Their ascent demonstrated that a human could reach Everest’s summit without bottled oxygen, a claim some earlier climbers had considered physiologically impossible.
Messner and Habeler divided the achievement across two summit teams. Habeler reached the top with Messner on 8 May, while Messner later made another oxygen-free summit attempt with Sherpa Ang Rita on 24 May. The expedition used no fixed supplementary oxygen system for the summit climbs.
The achievement is sometimes confused with Everest’s first ascent, completed by Edmund Hillary and Tenzing Norgay in 1953 using supplemental oxygen. It also differs from Messner’s later achievement of climbing all fourteen eight-thousanders.