Energon is the "life-blood" of all Transformers.
Energon is a blue liquid that fuels the Transformers' Sparks (their life source). As featured in the Dark of the Moon film, Energon is sometimes blue when it is in the form of a Transformer's blood. It can also be eaten, drunk, used as ammunition, and even currency (money). Another Energon-related object in the Dark of the Moon Film are "Energon Detectors," which are positioned in various locations Washington D.C., as revealed by Optimus Prime.