The presence of small amounts of sulfur (<500 ppm) on a Rh/Fe2O3/ZrO2 catalyst improves its water–gas shift (WGS) selectivity and stability under typical industrial conditions. Rh/Fe2O3/ZrO2 is a highly active WGS catalyst, but it produces small amounts of methane as a side product. The formation of methane is due to the presence of rhodium in the catalyst. Sulfur selectively poisons the site(s) responsible for methane formation. The improved selectivity and prolonged stability of the catalyst is maintained as long as sulfur is present.