A batch culture system for the production of citric acid by Aspergillus niger TISTR 3089 was studied to determine the effect of aeration and mixing on the volumetric oxygen transfer coefficient (kLa) and power requirement. A 2-1 batch stirred-tank was used with impeller speeds o f500-900 rpm at an aeration rate of 0.65vvm with glucose as the carbon source. kLa and power consumption varied with duration of fermentation. The data obtained were fitted to mathematical correlations between k{a and power requirement during gassing per unit volume of liquid (P/V) and superficial gas velocity reported by previous researchers. By including the agitator speed, better correlations were obtained, indicating the importance of stirrer speed in such correlations.The proposed relationship is: kLa - k (P/V) 095 UP 0.67 N0.5, where U is the superficial gas velocity and N is the stirrer speed.