In an internal loop airlift reactor of 55L working volume,the gas-liquid volumetric oxygenmass transfer coefficient k_Lα,gas holdup ε_G and liquid circulation time t_c were measured with the sol-ution of carboxymethyl cellulose(CMC)to simulate the performance of a reactor with highly viscousbroth.Electric conductivity and oxygen probes were used to measure the local gas holdup,liquidcirculation time and oxygen mass transfer coefficient in the individual sections of the reactor(riser,downcomer and the gas-liquid separating section at the top of the reactor)and the total reactor,respectively.The values of k_Lα for the riser,downcomer and separation sections of the reactor were alsoestimated and compared with that for the total reactor.The results show that,both k_Lα and ε_G in-crease but t_c decreases with increasing gas velocity.Correlations and comparisons with works reportedin the literature are also presented.Data show that the methods developed for k_Lα measurements inthe individual section and In an internal loop airlift reactor of 55L working volume, the gas-liquid volumetric oxygen mass transfer coefficient k_Lα, gas holdup ε_G and liquid circulation time t_c were measured with the sol-ution of carboxymethyl cellulose (CMC) to simulate the performance of a reactor with highly viscousbroth. Electric conductivity and oxygen probes were used to measure the local gas holdup, liquid circulation time and oxygen mass transfer coefficient in the individual sections of the reactor (riser, downcomer and the gas-liquid separating section at the top of the reactor) and the total reactor, respectively. These values ​​of k_Lα for the riser, downcomer and separation sections of the reactor were also solved and compared with that for the total reactor that results show that, both k_Lα and ε_G in-crease but t_c decreases with increasing gas velocity.Correlations and comparisons with works reportedin the literature are also presented.Data show that the methods developed for k_Lα measurements inthe indi vidual section and