The use of oxygen remains controversial. We removed all oxygen bottles from the mountain, and so for us the decision whether or not to use oxygen was based solely on ethical and esthetic grounds. We chose added safety over added challenge. Others continue to make different decisions.
Rate of supplemental oxygen consumption (this is really down in the details): I started at 2 l/min. and moved up to 2.5 l/min on the final climb up to the summit plateau. The other two in my group used .5 l/min more. Oxygen was turned off at all rest breaks and while on the summit. We were up and down so fast that I had over two thirds of my oxygen left when I got back to camp III.