This experimental work describes the influence of an impeller on hydrodynamics and mass transfer in an internal loop contactor. Contributions of each motion source (gas and impeller) are identified. Depending on operating conditions, these two factors may be additive and enhance liquid circulation or they may be opposite and reduce liquid velocity. For mass transfer, however, the impeller gives good results under some specific conditions, as the coefficient k(L)a becomes four times larger than the value obtained without mechanical agitation. The analysis of the different energy sources shows that the use of an impeller in this airlift can be justified when the gas flow rate has to be kept moderate.