A Calgary mountain climber who chose to summit Mount Everest without oxygen had the "athletic prowess" to attempt such a feat, according to a friend and fellow climber, who says he too would have gone without oxygen if he was just as fit.

Frank Ziebarth, 29, died on May 21 just below the summit of the world's tallest mountain as he was descending back to base camp.

Ziebarth chose not to use bottled oxygen for the 8,848 metre climb, which can ward off altitude sickness and its potentially fatal side effects.

"For me, if I had the strength and the athletic prowess to climb Everest without oxygen, I think I might have tried it," Manuel Pizarro told Canada AM on Wednesday. "I just don't have that kind of fitness level. Frank did."

Pizarro, who was part of the same climbing team as Ziebarth, reached the mountain's peak at 7:30 a.m. He crossed paths with Ziebarth on his way back down the mountain at around 9:00 a.m. about a kilometre from the summit's peak.

By then, Ziebarth was suffering from hypothermia and a lack of oxygen. He later died at the bottom of the mountain's third step.

Ziebarth, a German national who lived in Calgary, had previously climbed Shishapangma, Cho Oyu and Lohtse without oxygen, according to a statement posted at EverestNews.com.

Pizarro said that while climbing mountains without oxygen is "risky," many top athletes do it.

According to Pizarro, Ziebarth's fitness level would allow him to take about half the time to climb a distance than it takes other experienced climbers.

But going without oxygen is a goal of many passionate climbers so that they can make it as pure an experience as possible, Pizarro said.

"Frank was a purist at heart," Pizarro said. "He was adamant that it was him and the mountain."

What added to the risk, Pizarro said, was that there were fewer climbers on this trip than he'd seen on his previous Everest climb in 2007, meaning there were fewer resources available in case of an emergency.

More than 200 people have died on the mountain since it was first conquered by Sir Edmund Hilary and Tenzing Norgay in 1953.