Diesel engine oil soots from different engines have the appearance of carbon black but contain significant concentrations of engine oil additive elements. Evaluation of the soots in 4-ball wear tests supported the theory that the soots reduce the antiwear additive effectiveness by preferentially adsorbing the active antiwear additive components before they can form the essential antiwear surface coating rather than removing the surface coatings by abrasion after they are formed. Engine load and exhaust gas recirculation have large effects on the soot prowear characteristics, whereas engine refinements, engine make and oil type have lesser effects. No antiwear additives were found more effective than the currently used zinc dialkyl-dithiophosphates. Several preferential adsorber additives were effective in simple blends but not in fully formulated engine oils.