An improved gas permeation method for characterising microporous asymmetric hollow fibre membranes has been adapted in this study where the pore size distribution of the membranes was taken into consideration. Both standard normal and log-normal distribution functions were employed in the relevant equations. Parameters concerning membrane structures such as pore size, pore size distribution and effective porosity were determined through regression of analysis of gas permeation data. These parameters were then used to predict the permeation coefficients over a range of operating pressures. The predicted permeation coefficients were found to be in good agreement with the actual experimental data. The membrane structure parameters were also used in predicting the theoretical membrane's coefficients for comparison with H2S gas absorption experimental data. The results indicate that log-normal distribution function analysis is better off in producing a realistic predictions of membrane's coefficients, which are commonly used to indicate the efficiencies of membrane-based absorption for soluble gas removals.