Bearings serve to link machine parts with relative motion. Sometimes this primary role is exceeded with oil-film bearings, and the self-excited-vibration oil whip occurs. A stability criterion which includes the effect of rotor flexibility has been devised through an electric-analog study, and interpretation on the basis of bearing properties is in substantial agreement with test results, and experience with actual machines. In particular it is shown that rotor flexibility reduces the region of stable operation; however, the final question of stability depends on all system elements involved in the motion.