The effect of solids concentration and the presence of the charged polymeric additive Magna Floc LT25 on gas-liquid oxygen transfer and oxygen consumption rates have been evaluated for flocculent yeast cells grown in batch fermentations. No significant differences were found for oxygen consumption due to the presence of the additive. Low biomass concentrations have a positive effect oil oxygen transfer rate, when the additive was present in the medium. For biomass concentrations above 1 g/L, an increase in biomass concentration leads to a reduction on oxygen transfer rates regardless of the presence of the additive.