This paper describes the use of spiral groove gas lubricated bearings in a very high speed cryogenic expansion application. Previous experience using externally pressurized and tilting pad gas bearings is described followed by a qualitative description of the analytic methods used to predict the behavior of a rotor supported on spiral groove journal and thrust bearings. This involved not only the calculation of bearing stability and rotor critical speeds, but also detailed thermal and structural calculations to determine the changes in the small clearances. It is shown how, under certain cooling conditions, the bearing clearance reduced to unacceptable values, and shows how a simple increase in bearing clearance avoids this problem allowing successful operation. The paper concludes that modern theoretical techniques for both hydrodynamic and structural behavior are essential in the use of these high speed gas bearings.