Prince, I can assure you that supplemental oxygen is absolutely provided by portable oxygen bottles on many airliners (e.g. 767, 737, a320). Their fixed oxygen system is chemicallly generated and not capable of extended use. Aircraft with bottled emergency oxygen (e.g. 747, a380) still carry supplementary portable bottles.
Preflight, 'enough' supplementary oxygen is defined by the manufacturer, whereby the DDG may allow a reduction in accordance with the CAO 20.4 8.8 limit. Post dispatch, flight at 14000' is only limited by flight deck crew oxygen endurance. Bit of a thread drift, happy to chat over PM!
Last edited by *Lancer*; 6th Jan 2014 at 16:19.