Overall volumetric mass transfer coefficient (k(L)a) of carbon monoxide in a perfluorocarbon-distilled water mixture was evaluated in a dual impeller stirred tank bioreactor (Rushton-type and Smith-type). TWo agitation speeds (300 and 500 rpm), three specific gas flow rates (2.0, 2.5 and 2.7 vvm), two working volumes (0.75 and 1L) were tested, as well as four different liquid phase compositions: pure distilled water; distilled water and perfluorodecalin (PFC); distilled water and Tween (R) 80; and distilled water, PFC and Tween (R). 80. CO concentration in liquid phase was determined using a myoglobin bioassay technique and k(L)a and saturated CO concentration were determined using Maximum Likelihood Estimation (MLE) with a hybrid optimization strategy. A maximum k(L)a of 603.48 h(-1) was obtained at 500 rpm, 2.7 vvm and distilled water, PFC and Tween (R) 80 as liquid phase. Tween (R) 80 was responsible for increasing mass transfer when mixing these three components comparing to a liquid phase composed of PFC and distilled water (7 time increase at 2.7 vvm and 500 rpm), and pure distilled water (2.9 time increase at 2.0 vvm and 1.6 times at 2.5 vvm). Moreover, MLE proved to be a valuable tool to critically analyse experimental uncertainty in parameter estimation. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.