PFCs, also known as fluorocarbons, are inert, water-insoluble, synthetic compounds, consisting primarily of carbon and fluorine atoms bonded together in strong C–F bonds. PFCs are substantially clear and colorless liquid emulsions that are heterogeneous in molecular weight, surface area, electronic charge, and viscosity; their high content of electron-dense fluorine atoms results in little intramolecular interaction and low surface tension, making such substances excellent solvents for gases, especially oxygen and carbon dioxide. Some of these molecules can dissolve 100 times more oxygen than plasma. PFCs are naturally hydrophobic and need to be emulsified to be injected intravenously. Since PFCs dissolve rather than bind oxygen, their capacity to serve as a blood substitute is determined principally by the pO2 gradients in the lung and at the target tissue. Therefore, their oxygen transport properties differ substantially from those of whole blood and, especially, from those of RBCs. At a conventional ambient pO2 of 135 mmHg, the oxygen content of 900 ml/l perfluorocarbon is less than 50 ml/l, whereas an optimal oxygen content of 160 ml/l, which is still lower than that of whole blood in normal conditions, can be achieved only by a pO2 greater than 500 mmHg. In practice, at a conventional alveolar pO2 of 135 mmHg, PFCs will not be able to provide sufficient oxygenation to peripheral tissues.