It's getting ridiculous on Everest. Once you get above 8000 meters and into the "death zone", you obviously need supplemental oxygen. That's no problem as long as you can keep moving to the summit, and head straight back down.
The problem today, they get these traffic jams on the ropes, and climbers are forced to wait sometimes several hours, for other climbers to summit and descend.
Many end up running out of oxygen due to the wait time and end up becoming oxygen starved. If they don't get dragged back down the mountain to a safe altitude, they die.
Anyone ever read the story about "Green Boots" ? This guy has been on the mountain since 1996.