Geri Winkler along with others from Alpine Ascents reached the summit of Cho Oyu yesterday.   Looks like Geri succeeded in doing it without supplemental O2.

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Here is from the Alpine Ascents cybercast:
 
Cho Oyu Team Summits!
September 30, 2009    

We just received word from Michael Horst (Expedition Leader) that our team has made the summit of Cho Oyu and is now back at Camp 2 resting. Everyone is doing fine, and the group will descend to base camp tomorrow. We want to congratulate our climbers John Burns, Vanessa Folkerts, Michael Girard, Martin Grieder, Geri Winkler, Jan Smith, along with guides Michael Horst & Lakpa Rita Sherpa, and the climbing Sherpa team of Tshering Dorjee Sherpa, Kami Rita Sherpa, Fur Kancha Sherpa, Passang Rita Sherpa. Michael reported fantastic weather conditions on summit day, and the weather is forecasted to hold during their descent to base camp.