A gas giant was a type of planet that was primarily made up of gaseous layers. Most were made primarily of hydrogen and helium, with some methane; a rare few had oxygen-rich layers within their atmospheres which were capable of supporting a life zone. Gas giants usually had many moons due to their high mass and gravity, and some also possessed spectacular systems of planetary rings. Famous gas giants included Bespin, Endor, Taloraan, Yavin Prime, and Oovo. The Galactic Empire had classified gas giants based on a type gas giant that they could be compared to such as Bespin-class gas giants.