Abstract: An apparatus for injecting a chemical additive into a fluid flow stream. In one embodiment, liquid petroleum fuel is being pumped from a storage unit into a tank of a tank truck and a controlled amount of a fuel additive is injected into the flow stream of the petroleum fuel. Preferably, the petroleum fuel is pumped through a line from the storage which is quick-connected to a loading line attached to the tank truck. The chemical additive is pumped from a supply container on the tank truck into the loading line by means of air pressure supplied to the additive container from the tank truck's own air pressure supply system. The fuel additive is pumped at a controllable rate and at a higher pressure than the pressure of the fuel stream.