Water-Gas Shift Reaction experiments were conducted in membrane reactors with pure Pd and Pd-Cu alloy as membrane materials at conditions similar to those encountered in the outlet of a gasifier. The effect of common gasifier products such as CO, H2O, and H2S on the hydrogen permeance through Pd and Pd-Cu alloy membranes was investigated. Results indicate that H2O had negligible effect on hydrogen permeance through both Pd and Pd/Cu alloy membranes, while H2S and H2O were observed to moderately reduce hydrogen permeance through certain Pd/Cu alloys membrane and severely compromise the function of Pd membranes.in permeance when exposed to hydrogen sulfide under bcc phase stability conditions.