This paper deals with a perfectly cylindrical, self-acting, gas-lubricated, and unloaded journal bearing. Complete stability criteria for the translational mode of oscillation are formulated and a method is given by which the ultimate stable operating speed may be found for arbitrary ambient pressure, viscosity, and bearing geometry. The nature of the stable motion is indicated. In addition, a simplified criterion and bearing motion are given for low-speed operation. Graphs which show the effect of design parameters on bearing forces are included as an aid in numerical calculations.