In this work were determined in a stirred tank system with the phases non-miscible silicon oil and heptamethylnonane, the mass transfer volumetric coefficient (KLaH) of naphthalene and phenanthrene (liquid-liquid system). The KLaH values were correlated with the Reynolds number, observing that KLaH let of be a function of the Reynols for values NRe³17,000. The values reached of KLaH were 52 and 44 h-1 for naphthalene and 69 and 62 h-1 for phenanthrene both with silicon oil and heptamethylnonane respectively. Also was evaluated the volumetric charge effect of the non-miscible solvents, in the volumetric oxygen transfer coefficient (kLa) for the same stirred tank system with aeration (liquid-liquid-gas system). The addition of each one of the solvents led to strong decrease of the kLa, being more marked the effect with the increase in the volumetric charge of the solvents. The kLa in the aqueous medium without solvent decreased of a maximum of 49 h-1 up to minimums of 22 h-1 with oil silicon and 7 h-1 with heptamethylnonane, in both cases with a volumetric charge of 5% of each solvent. The decrease in the kLa was probably due to a negative effect of the dynamic and kinematic viscosities of both solvents over: the oxygen diffusivity, thickness of the boundary layer and the specific interfacial area of the bubbles air.