The aim of this study is to experimentally investigate the characteristics of oxygen transfer efficiency in a vertical-up aeration process. The input power was calculated by measuring the electric voltage and current directly and estimated using the indirect Bernoulli balance technique. It was found that the increasing rate of the volumetric oxygen transfer coefficient was higher with an increase in the suction air flow rate than that with an increase in the primary flow rate. With an increase in the primary flow rate, the oxygen transfer efficiency decreased because the increasing rate of input power was higher than that of the volumetric oxygen transfer coefficient. It was found that the oxygen transfer efficiency obtained via the indirect Bernoulli balance technique was up to 4.4 times higher than that obtained by direct measuring technique.