Carbon monoxide adsorbs on the clean tungsten (112) face with an initial sticking probability of >0.9 at room temperature and desorbs with heat in three stages, the with about in each state at maximum coverage. Room temperature adsorption is nondissociative and almost random. Heating a CO covered surface produces well defined and “Complex” structures. The does not contribute directly to any diffraction pattern. The β1 is associated with the structures, and an irreversible temperature activated conversion at about 1000°K produces β2 molecules; these are responsible for the and Complex structures. Experiments with (112) substrates containing adsorbed oxygen show that does not react to produce , that does not adsorb onto an adsorbed oxygen atom and that in the presence of oxygen not all exposed tungsten atoms adsorb . The (112) surface is composed of two exposed (112) planes, and by covering only the second layer tungsten atoms with oxygen, it was found that adsorbs on the topmost layer as well as on the second layer. Molecules adsorbed on the top layer desorb as β1 and the maximum number of β2 molecules on the surface was proportional to the number of second layer tungsten atoms not covered by oxygen.