The mass transfer characteristics of bubbly flows in co-flowing and T-junction microchannels are described in this study. A CO2-N-2 gas mixture and a monoethanolamine-ethylene glycol solution were used as the gas and liquid phases, respectively, to generate gas/liquid bubbly microflows. The bubble dimensions changed obviously during the bubble-forming and bubble-flowing stages. The overall mass transfer coefficients (K-L) at these stages were determined by developing an online measurement method through which time-dependent changes in bubble volume were analyzed. Investigation of the effects of phase flow rate and concentration of the two phases on K-L showed that K-L was in the range of 1 x 10(-4) -4.9 x 10(-3) m/s. In addition, empirical correlations were established to predict K-L for different mass transfer stages. (C) 2014 Elsevier Ltd. All rights reserved.