For the in situ growth of cuprate superconductors and related oxides by vacuum deposition methods it is desired to achieve as high a flux of oxidizing species as possible at the growing surface and as little as possible elsewhere within the reaction chamber. The well known gas flow equations derived by Knudsen, Clausing, and others which apply to the molecular flow regime were implemented in a computer algorithm to simulate the gas flow upon a substrate from hypothetical nozzles of several different geometries. The optimal design for a particular MBE chamber and substrate size was determined and such a nozzle was fabricated and characterized. A dysprosium-coated quartz crystal monitor was used to determine the oxidant flux. The measured result matches predictions of the computer model within a factor of three. The computer algorithm was also used to model the spatial distribution of ozone gas through a nozzle of another reported geometry, where measurements of the resulting flux had been made. The shape of the calculated flux distribution agrees to within a few percent and the absolute values of flux reported agree within a factor of two.