Abstract: The duration of a pumping operation from a fixed supply of cryogenic liquid is extended by minimizing the amount of cryogenic liquid which is recirculated between a primary cryogenic pump and a storage tank for containing the cryogenic liquid. The primary cryogenic pump is characterized by a minimum necessary net positive suction head at its intake. The net positive suction head of the cryogenic liquid is directly measured at the inlet of the primary cryogenic pump by means of a differential pressure gauge. The total pressure on the cryogenic liquid at the inlet of the primary cryogenic pump is then maintained by means of a cryogenic booster pump to always exceed the measured vapor pressure at the inlet by an amount just equal to the minimum net positive suction head required by the primary cryogenic pump.