Numerical analysis is presented for gas absorption accompanied by a second-order reaction into a liquid layer of finite thickness in laminar flow, with the gas-phase mass transfer resistance and the axial decrease of the gas-phase solute concentration due to absorption being taken into account. Both cocurrent and countercurrent flow modes are analyzed, where the presence of significant resistance or axial decrease of the solute concentration in the gas phase can lead to substantially lower rates of gas absorption than those found when the influence of gas-phase mass transfer is not considered. Approximate expressions describing the exact numerical solution to the enhancement factor in the cocurrent flow mode are developed and can be extrapolated for estimating the enhancement factor in a more general case of a (1, n)-th-order reaction in which the influence of gas-phase mass transfer cannot be neglected.