Tests were conducted to investigate the effects of surface treatments on the tribological characteristics of Monel K-500 being rubbed in high-pressure oxygen. The surface treatments investigated were ion-implanted oxygen, chromium, lead, and silver, electrolyzed chromium, and electroless nickel silicon carbide composite. The sample temperatures observed during frictional heating tests in ambient oxygen pressure were significantly higher than during tests at 6.9 MPa (1000 psi) oxygen pressure at the same loads and speeds. The ion-implant treatments reduced the average coefficient of friction at low contact pressure; however, this was eliminated when the contact pressure was increased from 5 to 20 kN/m2 (50 to 200 psi). Total sample wear was greater at 6.9 MPa (1000 psi) than at ambient oxygen pressure except when chromium was present. Electrolyzed chromium dramatically increased the total sample wear of Monel K-500 while other surface treatments affected sample wear only moderately. While some useful observations could be made from the data generated using this test apparatus, a different method must be developed if a more sensitive assessment of the effects of surface treatments on the tribological characteristics of Monel K-500 is required.