A system and method of administrating conventional hyperbaric chamber therapy as well as supplemental oxygen therapy at ambient conditions to an animal using a veterinary hyperbaric chamber. The hyperbaric chamber can function in its usual mode of operation; i.e., providing oxygen at greater than atmospheric pressure and also in a second mode of operation to administer supplemental oxygen thereafter at ambient pressure conditions. In the second mode of operation, the method and apparatus may deliver approximately 80 liters per minute continuous flow of 0.21 through 1.0 FI02 adjustable oxygen gas mixture. The mixture is delivered at ambient pressure from one end of the chamber, flows across the animal positioned within the hyperbaric chamber, and exits at the opposite end for exhaust to ambient conditions. A high flow gas mixture is utilized to maintain accurate gas mixture concentrations with fluctuating supply pressures of medical air and medical oxygen gases.