The dynamic pressure method (DPM) is used for measurement of k(L)a in a 1-m(3) pilot scale fermenter in coalescing (distilled water) and noncoalescing (0.3 M Na2SO4 aqueous solution) batches. The method consists in recording oxygen concentration in a batch after a small pressure change (20 kPa) in the fermenter. The upward pressure change is brought about by temporary closing and subsequent throttling of outlet gas stream and the downward change by full reopening of the gas outlet. Absorption of pure oxygen yields the same k(L)a values as absorption of air. In noncoalescing batch, the downward k(L)a values are always higher than the upward values owing to spontaneous nucleation of bubbles. The experiments performed in a stirred cell confirm this behavior. Thus, only upward pressure change should be used for measurement. The correlations of k(L)a data measured in small (18-L) and large (1000-L) vessels based on power dissipated and superficial gas velocity are in a good agreement. Unlike the DPM, the classical dynamic methods yield, under the same conditions, excessively low values of k(L)a (the dynamic startup method) or fail to produce data at all (the dynamic method with interchange of air for N-2).