The fluid pressure between two parallel circular plates separated by a relatively thin film of oil was measured during sinusoidal axial vibration of the top plate. The results of the experiment were compared with those predicted by inertialess considerations and an approximate solution which considers the fluid inertia. On the basis of this investigation, in which Reynolds' number was varied up to a value of three, the inertialess solution gives good results for the film pressure for Reynolds' number up to about 0.4; at higher values, pressures greater than those predicted by inertialess considerations were obtained. An approximate solution considering the fluid inertia is shown to be in good agreement with the test data which can be represented by a third-degree polynomial equation.Contributed by the ASLE Technical Committee on Bearings and Bearing Lubrication and presented at the Annual Meeting of the American Society of Lubrication Engineers held in Chicago, Illinois, May, 1964.