Using the standard deviation of pressure fluctuations to find the minimum fluidization velocity, U-mf, avoids the need to de-fluidize the bed so U-mf can be found for operational bubbling fluidized beds without disrupting the process provided only that the superficial velocity may be altered and that the bed remains in the bubbling fluidized state. This investigation has concentrated on two distinct aspects of the pressure fluctuation method for U-mf determination : (1) the minimum number of pressure measurements required to obtain reliable estimates of standard deviation has been identified as about 10000 and (2) pressure fluctuation measurements in the plenum below the gas distributor are suitable for U-mf determination so the problems of pressure probe clogging and erosion by bed particles may be avoided.