Gas

Gas was a state of matter that expanded to fill a space. Gases could be invisible, such as oxygen, or could appear as a visible, misty substance, such as Clouzon-36. Many terrestrial planets had an atmosphere, a collection of gases that formed a relatively thin veil over the world's surface, while gas giants were composed almost entirely of gas. Gas mines such as Bespin's Cloud City were used to extract and purify gases from a planet's atmosphere. Most living organisms required gas to breathe, while some gases were poisonous to certain species. Some gases could also be used as drugs, such as to render individuals unconscious.

Gases included:
 * Ammonia
 * Clouzon-36
 * Dioxis
 * Durilliam
 * Hydrogen cyanide
 * Kesium gas
 * Knockout gas
 * Methane
 * Oxygen
 * Ozone
 * Rethen
 * Tibanna
 * Vanoorian ammonia