Medline Plus states normal oxygen levels for a human at sea level are 94 to 100 percent saturation. Another oxygen value taken is the partial pressure of oxygen and the normal values for it are 75 to 100 millimeters of mercury. Oxygen readings are lower at altitudes above 3,000 feet.
WebMD states oxygen values are obtained through an arterial blood gas test. This test is performed to check on lung function and screen for severe lung or breathing diseases, such as cystic fibrosis, asthma, and chronic obstructive pulmonary disease. This test also measures the acidity of the blood and levels of other blood gases.