This chapter continues the mass transport to the specific case of oxygen and the role of hemoglobin. The oxygen hemoglobin dissociation curve is presented along with the Hill equation, which can be used to describe how the hemoglobin oxygen saturation depends on the oxygen partial pressure in the blood. Oxygen mass balance relationships are then presented. Oxygen transport in blood oxygenators, bioartificial organs, tissue engineered constructs, and perfusion bioreactors is also given. The Krogh tissue cylinder model is then used to describe oxygen transport between the capillary and the surrounding tissue. The oxygen transport by artificial blood is also discussed.