Oxygen saturation or dissolved oxygen (DO) is a relative measure of the amount of oxygen (as O₂) which is dissolved in a given medium.

It can be measured with an oxygen sensor. The standard unit of oxygen saturation is percent (%).

Fish, invertebrates, plants, and aerobic bacteria all need oxygen (dissolved in water) for respiration. In medicine, oxygen saturation refers to oxygenation. This means when oxygen molecules (O₂) enter the tissues of the body. Normal arterial blood oxygen saturation levels in humans are 95–100 percent. If the level is below 90 percent, it is considered low and called hypoxemia. view more...