Five-degree-of-freedom (5-DOF) characterization of the stability of a gas-lubricated conical bearing of the spiral-groove design is presented for bearing numbers up to 500. Critical points in stability analysis are identified in impedance contour plots separately for axial, cylindrical, and conical modes. The stability thresholds with respect to each mode are graphed as functions of the bearing number. For axial and cylindrical modes, the threshold parameter is the rotor mass. For the conical mode, the threshold parameter is an equivalent mass that is dependent on both transverse and polar radii of gyration of the rotor. An application example illustrates a rational procedure to specify nominal bearing clearance and its allowable tolerance range.