WebBusinesses and organisations. Vehicles and vessels. Other uses. See also. O2. Look up O₂ in Wiktionary, the free dictionary. O2, O-2, o2, O2, O2, O2− or O2+ may refer to: Science and technology. O2 or dioxygen, the common allotrope of the chemical element oxygen. O2−, the ion oxide. O− 2, the ion superoxide. O+ 2, the ion dioxygenyl.