A portable gas delivery system is provided to provide oxygen or other gaseous mixture for use in emergencies, athletic events, and similar activities. The portable gas delivery system includes a regulator with an accumulator chamber disposed within the regulator and adjacent a mixing chamber. The accumulator chamber receives oxygen or other gas from a replaceable gas source such as a cylinder. The mixing chamber mixes ambient air and gas from the cylinder to form a gaseous mixture which is inhaled by a user. Each use of the portable gas delivery system may be in metered burst of predetermined duration and/or frequency or may be substantially continuous as provided for in the accompanying method.