In the present work, a simple analytical solution of the simplified mass conservation equations applicable to the calculation of the volumetric mass transfer coefficient (k(L)a) in gas-liquid systems, named the absorption model (ABM), has been proposed and compared to the classical and less complete continuous stirred tank reactor model (CSTR). A partially aerated 2D bubble column has been used in order to study the hydrodynamics and mass transfer at varying superficial gas velocities and aspect ratios (H/W) and examine the benefits of the proposed model. In addition to its simplicity and on the contrary to the CSTR model, the ABM is able to capture the variation of kLa with H/W caused by the formation of additional liquid circulation cells as H/W is increased. Furthermore, the ABM kLa resulting values, that are comparable with previously reported ones, increase with increasing axial positions as a result of higher aeration at upper sections of the bubble column. Also, k(L) values, not frequently reported in the literature, were calculated. The results show that kL remains approximately constant (approximate to 5.5 x 10(-4) m/s) and, therefore, independent of U-G in the considered range.