Sliding experiments are conducted with a graphite pin on copper, iron and phosphor bronze disks at a constant sliding speed (0.76 m/s), load (11.5 N), and sliding distance(10 km) without lubricants. Ambient(RH 30-50%), dried air, nitrogen and vacuum(1×10−3 Pa) atmospheres were tested. The amount of adsorbed atmospheric gases depend strongly on the crystallographic orientation of graphite. The results show also that the friction and wear characteristics are affected by the concentration of the surrounding gas being adsorbed on the transferred graphite on the disk. It is found that there is an optimum concentration of adsorbed gas at about 5% to minimize the friction coefficient.