Donor blood is a limited resource and its transfusion is associated with significant adverse effects. Therefore, alternatives have been searched, the ultimate being artificial oxygen (O2) carriers. There are two main groups of artificial O2 carriers: hemoglobin based and perfluorocarbon emulsions. The hemoglobin molecule in hemoglobin based artificial O2 carriers needs to be stabilized to prevent dissociation of the α2β2-hemoglobin tetramer into ab-dimers in order to prolong intravascular retention and to eliminate nephrotoxicity. Other modifications serve to decrease O2 affinity in order to improve O2 off-loading to tissues. In addition, polyethylene glycol may be surface conjugated to increase molecular size. Finally, certain products are polymerized to increase the hemoglobin concentration at physiologic colloid oncotic pressure. Perfluorocarbons are carbon-fluorine compounds characterized by a high gas dissolving capacity for O2 and CO2 and chemical and biologic inertness. Perfluorocarbons are not miscible with water and therefore need to be brought into emulsion for intravenous application. Development, product specification, physiologic effects, efficacy to decrease the need for donor blood in surgery and side effects of the following products are described: Diaspirin cross-linked hemoglobin (HemAssist), human recombinant hemoglobin (rHb1.1 and rHb2.0), polymerized bovine hemoglobin-based O2 carrier (HBOC-201), human polymerized hemoglobin (PolyHeme®), hemoglobin raffimer (Hemolink™), maleimide-activated polyethylene glycol-modified hemoglobin (MP4) and perflubron emulsion (Oxygent™). In addition, enzyme cross-linked poly-hemoglobin, hemoglobin containing vesicles (nano-dimension artificial red blood cells) and an allosteric modifier (RSR13) are discussed. The most advanced products are in clinical phase III trials but no product has achieved market approval yet in the US, Europe or Canada.