an apparatus for rapidly filling a pressure vessel such as a fuel storage tank with highly pressurized gas by initially inserting into the tank , a measured quantity of liquefied natural gas or some other type of cryogenic liquid and permitting the temperature of the liquid to rise within the tank to vaporize it into a gas under a pressure which at least approaches the design working pressure of the tank . the storage tank maintains the gas under sufficiently high pressure that automotive fuel tanks or other small tanks can be rapidly filled from the storage tank without compressors due to the high internal pressure of the storage tank .