Surface effects in the reactions of dissociated hydrogen–oxygen systems and the products condensed therefrom have been investigated. Water vapor at about 0.1 Torr was streamed at high velocity through an electrodeless discharge confined in tubes of different materials or with various surface coatings. In all cases the products trapped in liquid nitrogen evolved oxygen gas on warming, but the relative amounts varied considerably from one type of surface to another. In some cases there was clear evidence that the walls of discharge tube were attacked by hydrogen atom bombardment. The decomposition, both thermal and electrical, of pure hydrogen peroxide vapor was studied likewise. The pyrolysis products gave off very little oxygen on warming. By contrast the products from electrical decomposition, even at low power level, evolved much oxygen, most of it above the melting point.It is concluded that there is always some decomposition of hydrogen peroxide in the trapped products. However, this does not seem sufficient to account for all the evolved oxygen; at least not in the case of dissociated water vapor.