Background: For NPPV machines that add oxygen, the administered oxygen concentration is unknown and the oxygen concentration may differ from the one supplied. Method: Using 3 models, we experimentally verified the oxygen concentration depending on the model, ventilation rate, and oxygen addition site by varying the supplied oxygen flow rate of 2 L/min, 6 L/min, and 10 L/min. Results: No differences were observed in oxygen concentration depending on model or ventilation volume. There were differences in oxygen concentration depending on the location of oxygen addition. Conclusion: Even with the same oxygen administration flow rate, the oxygen concentration differs depending on the oxygenation site.