Barrel

A Barrel is the placeholder name given to an item seen in the E3 trailer. Barrels are seen moving between Storage Tanks and Oil Plants (both of these are guesses as to the function of the structures).

Speculation
So far, as we have not seen any pipes, the assumption is that all liquids exist only as barrels which can be sent between machines on belts. The only liquid that is currently suspected seems to be oil, due to what seem to be oil plants.