Paralithium was a substance which was used as fuel for some ion-based propulsion systems, and which could be converted into trilithium.

In 2373, the USS Voyager was able to locate a cargo vessel in the Akritirian system which was using this fuel by locating their paralithium plasma emissions. It was later determined that the ship's two inhabitants, Vel and Piri, had used their paralithium fuel to create a trilithium explosive, and supplied it to the terrorist organization known as "Open Sky." (VOY: "The Chute")