
Indeed so; it's at the extreme limit of what is humanly possible.  It is
possible only because Mount Everest is at a fairly low latitude:  there
is a slight equatorial bulge in the atmosphere -- beyond what is induced
by the Earth's rotation -- thanks to the overall circulation pattern of
the atmosphere (air cools at poles and descends, flowing back to equator
where it is warmed and rises), and this helps just enough to make Everest-
without-oxygen feasible.  Only just feasible, mind you:  the guys who did
it reported hallucinations and other indications of oxygen starvation,
and probably incurred some permanent brain damage.