The results of life tests of 388 caged, needle-roller bearings under combinations of load, speed, and amplitude of oscillation are analyzed with Weibull statistics. The rolling bearing theory of Lundberg and Palmgren is extended to cover oscillating roller bearings and is favorably compared with the life tests. A formula for basic dynamic capacity in oscillation is developed for amplitudes of oscillation which are less than the critical amplitude. Capacity formulas are also presented for both ball and roller bearings for any amplitude of oscillation.