George Patterson wrote:
No. 12,500' if you exceed it for 30 minutes or 14,000' if you go over
that at all. At 15,000', passengers also have to be on oxygen. Section
91.211.

actually the passengers must be *provided* with oxygen; notice
the different wording between 91.211(a)(2) and 91.211(a)(3);
i.e., your passengers do not have to be *on* oxygen (makes
for much quieter passengers, and saves on o2 refills :-)))

--Sylvain