The gas-liquid mass transfer volumetric coefficient k(L)a for an EGSTAR agitator, which has been practically used as a bioreactor, is measured. The effect of geometries (i.e., hole fraction, pitched paddle width, draft tube height) on k(L)a is clarified experimentally. k(L)a depends only on the power consumption per unit volume (P-av + P-gv), regardless of the hole fraction and the pitched paddle width in the power region of (P-av + P-gv) = 0.5 similar to 4.0 kW/m(3). As the draft tube height of EGSTAR agitator is lower, the power consumption at the transition point from bubbling controlling to agitation controlling is lower.