This report is intended to acquaint personnel involved in the design, inspection, and maintenance of civil transport oxygen systems with the human respiratory requirements and oxygen system design considerations necessary to effect an interface and provide acceptable high-altitude life support. Simplified explanations and language that should be understandable by lay and semiprofessional engineering personnel are used, with references to sources of more detailed information. The oxygen system designer is directed to applicable Federal Aviation Regulations pertaining to oxygen systems and, where regulatory guidance does not exist, directs the reader to applicable oxygen equipment industry practices, standards, and information reports. (Author).