Cavitation thresholds of 5W30 and 10W30 oils were measured in laboratory experiments using electrically-driven disks of piezoelectric ceramic as sources of mechanical excitation. The technique allows the mechanical-wave power density at which cavitation begins to be observed and calculated from electrical quantities and the volume of the oil sample being tested. Both cavitation turn-on and turn-off thresholds have been measured as functions of temperature and frequency. The temperatures ranged from 20 to 100°C and the frequencies ranged from 50 kHz to 4 MHz. The experiments have shown these oils can be made to undergo cavitation at surprisingly low thresholds.