High-speed motion picture camera experiments on dynamically loaded journal bearings revealed the development of vapor cavitation. The parameters studied were the length-to-diameter (L/D) ratio of the bearing, the surface velocities of the journal and bearing, the surface materials of the roller, and the static and dynamic eccentricities of the bearing. The occurrence of vapor cavitation is clearly evident in the films. Vapor cavitation occurred when the tensile stress applied to the oil exceeded the tensile strength of the oil or the binding of the oil to the surface. The physical situation necessary for vapor cavitation to exist was a squeezing and sliding motion within a bearing.