A mathematical model is developed to study the various transport steps associated with the degasification of a dissolved gas from water using a hollow fiber membrane contactor (HFMC) operated in liquid-liquid extraction mode. The model analysis considers the conservation rate equations for the gas, incorporating axial and radial diffusion through the lumens, Knudsen diffusion through the membrane-pores, and the adsorption and desorption of the gas molecules at the pore walls. The model results are found in reasonably good agreement with the experimental data obtained in this study for the degasification of ammonia (NH3) from water using a polypropylene HFMC, with aqueous sulfuric acid solution as the extractant. In addition, the separation rate is shown to be dependent on the solution pH and independent of the initial NH3 concentration in the range of 200-1500 ppm. The removal efficiency of the HFMC for the degasification of NH3-water is found to be 99% or more under the different operating conditions selected. The average molar flux of 12 x 10(-5) mol/s-m(2) calculated in the present case is comparable to the literature values and suggests the potential to scale-up the studied HFMC system. (C) 2011 Elsevier B. V. All rights reserved.