An unsteady-state model for predicting mass-transfer coefficient k(L) of bubbles with mobile surface was developed for turbulent gas-liquid dispersions. This model was derived from an unsteady-state convection and diffusion equation through a characteristics method. Unlike the previous work, this model considered the contributions of the amount of fluid structures of different scales (i.e., eddies) existing in the turbulent flows, the frequency of eddies arriving at the surface, the deformation and oscillation of bubbles to mass transfer. This model was based on the framework of wide energy spectrum and can account for the role of eddies of different sizes in mass transfer. Thus the assumption adopted by the previous models that mass transfer was controlled by eddies of certain sizes is no more needed. The overall k(L) predicted by the proposed model showed a better agreement with the reported experimental data. (c) 2015 American Institute of Chemical Engineers AIChE J, 62: 1007-1022, 2016