Oxygen saturation, measured by pulse oximetry (SpO 2), is a vital clinical measure. Our descriptive, cross-sectional study describes SpO 2 measurements from 6289 healthy subjects from age 1 to 80 years at 15 locations from sea level up to the highest permanent human habitation. Oxygen saturation measurements are illustrated as percentiles. As altitude increased, SpO 2 decreased, especially at altitudes above 2500 m. The increase in altitude had a significant impact on SpO 2 measurements for all age groups. Our data provide a reference range for expected SpO 2 measurements in people from 1 to 80 years from sea level to the highest city in the world.