Previous studies have demonstrated that the durability of some fuel injection systems on compression-ignition engines will be adversely affected by fuels of sufficiently low lubricity. However, no widely, accepted lubricity measure is available; indeed, the wear mechanisms present have not been conclusively defined. The results of the present study indicate that oxidative corrosion is the predominant mechanism with very highly processed fuels, resulting in catastrophic wear and rapid failure. Less highly refined fuels contain natural corrosion inhibitors and produce alternate wear mechanisms that may still affect long-term durability. A laboratory test procedure directed toward the oxidative wear mechanism was evaluated and a number of modifications suggested. The resulting test produced good correlation with the full-scale pump and appeared to correlate with the criteria necessary for oxidative corrosion. However, it is recognized that this single test procedure may not fully define the lubricity requirements of the injection system, particularly in the absence of oxidative corrosion or very highly loaded contacts that are susceptible to adhesive wear and scuffing.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993