What percent oxygen does a non-rebreather provide?

• A. 60% - 70%
• B. 80% - 90%
• C. 90% - 100%
• D. 100%

Answer: (C)

A non-rebreather mask can deliver very high concentrations of oxygen because the reservoir bag is filled with oxygen and is inhaled on each breath, while exhaled air escapes through side ports, limiting dilution with room air. When the flow is set high (typically about 10–15 L/min) and the mask fits well, the inspired oxygen concentration is around 90–100%. In practice, leaks, a poor seal, or very heavy breathing can reduce that value toward the 80–90% range, so while nearly 100% is possible, it is not guaranteed. This is why the best answer is 90–100%.