Hydrogenation of carbon monoxide at 101.3 kPa has been studied over a series of ion-exchanged Ru catalysts supported on NaX, NaY, KL, Na mordenite, and HY zeolites. The type of zeolite had pronounced effects on the activity and selectivity of the Ru. The specific activity would appear to be related to the dispersion of reduced ruthenium in the zeolite. Methane selectivity, however, seems to be strongly influenced by the type and concentration of alkali cations remaining in the ion-exchanged zeolite. These cations appear to promote chain growth much as traditional alkali promoters would, though perhaps more indirectly. Due to bifunctional properties of the zeolite-supported catalysts, a significant fraction of C4 was in the form of isobutane. Formation of isobutane seems to be related to either the Si Al ratio in the zeolites or the concentration of the remaining alkali cations, but not to the OH concentration. In addition, H2 chemisorption at 25 °C was increasingly suppressed as the Si Al ratio of the zeolite support increased. Both the formation of isobutane and the suppression of H2 chemisorption may be related to the acid strength of the OH groups present, which is a function of the Si Al ratio of the zeolite.