Gas-liquid mass transfer has been studied theoretically in a microprous hollow fiber membrane module operated under partially wetted conditions in the laminar flow regime. Dissolved oxygen removal has been used as an example for the simulation study. The mathematical model developed consists of nonlinear partial differential equations and is solved using the orthogonal collocation technique. The effect of membrane wetting pressures on the overall mass transfer performances of the module has been examined. The results indicate that under partially wetted operating mode, a maximum overall mass transfer coefficient is attainable with respect to the water velocity, which is completely different from the results obtained under both wetted and nonwetted conditions where the overall mass transfer coefficient is generally increased with water velocity. The phenomena of partial wetting of the membrane may provide an explanation to the observation that the overall mass transfer coefficient is increased to a maximum value and then is decreased with water velocity in a gas-liquid contactor.