Abstract: A portable hyperbaric chamber is provided that allows a person to perform endurance exercise at barometric pressures of from 0 to 10 lbs./square inch greater than ambient. The chamber is portable, semi-spherical and inexpensively constructed of an essentially air-impermeable, flexible material. This invention is a closed circuit rebreather using an oxygen supply and carbon dioxide removal means to provide an extended period of breathing without the need for attention to maintaining a fresh air supply. This system is designed for ease of use, low cost, and light weight. It utilizes reusable parts and a limited use pressure chamber and breathing bladder. This system features a lightweight pressure holding closure system which does not rely on expensive zippers and is stored in the pump unit which pressurizes it.