Abstract: An anti-theft device for preventing unauthorized removal of liquid from large volume liquid storage tanks. The anti-theft device comprises a tube-like stanchion positioned within the fill tube associated with the storage tank, such that the lower end of the stanchion rests upon the bottom of the tank. The stanchion includes a grid-like baffle positioned above the highest liquid tank level for preventing insertion of a siphon tube. A plurality of crimped projections extending inwardly from the inner circumference of the speed tube positioned between the stanchion and the fill tube to prevent upward withdrawal of the stanchion from within the fill tube. The speed tube is held in place by means of a rotatable collar threadedly secured to the upper end of the fill tube, and locked in place by means of a keyed set screw.