An investigation has been made on the amounts and composition of gases enclosed in West Greenland glaciers ranging from the Thule area near lat. 77° N. to Brede Fjord at lat. 62° N. In general, the gas composition deviated appreciably from that of air, and also varied within each piece of ice. Presumably these variations are caused by melting either in the firn area, or, more often, at the outlet sites. 13C analyses indicate that organic contamination of the snow may be another factor. Undisturbed ancient atmospheric air was therefore not encountered in our Greenland samples, but indications are that it might be found in the much colder Antarctic ice sheet. Gas bubbles analyzed from crack fills in icebergs had high oxygen concentrations, sometimes almost matching that of air-equilibrated ice-cold water, from which they undoubtedly originated. Blue icebergs, which often were seen floating up from the bottom of glacier fronts, also tended toward high oxygen concentration and very likely, therefore, are caused by freezing of melt water seeping down and collecting underneath the glacier.