The Dynamic Pressure-step Method (DPM) is based on recording time profiles of oxygen concentration in liquid as a response to a concentration change in gas invoked by a small change of overall pressure in the vessel. In contrast to earlier methods (standard dynamic method with inlet gas exchange, or start-up method) the concentration change is performed simultaneously and homogeneously in all bubbles of dispersed gas. The measurements were performed in a vessel of liquid volume 20 1 with aspect ratio (H/D) equal to 4 equipped with four Rushton turbines on a common shaft. In experiments, coalescing (distilled water) and noncoalescing (sodium sulphate solution) batches were used, both aerated by air or pure oxygen. Independent experiments with tracers showed the significant axial dispersion in both phases. The experimental k(L)a values (a) do not depend on oxygen concentration in the gas used, (b) exhibit a simple power dependence on the dissipated power and (c) in this correlation agree within 30% with those obtained in geometrically different vessels. Similar k(L)a measurements performed by using the standard dynamic and start-up methods produced substantially different results. In the noncoalescing batch experiments, the k(L)a values even exhibit a decrease at higher mixing intensities.