A series of studies was conducted in the jour-ball wear tester to better define the roles of volatility, environment, and polar impurities in boundary lubrication. A number of well-defined, super-refined mineral oils, free from polar impurities, were utilized as base stocks for these studies. The effect of volatility as a factor in wear is conclusively shown. Volatile base stocks were used to illustrate the effects of less volatile polar and nonpolar impurities. The relative importance of volatility of lubricity additives is also demonstrated. Methods for the quantitative measurement of dissolved gases including oxygen in the lubricant under practical test conditions are illustrated. The relationship between dissolved oxygen and wear is shown for several lubricants. The interrelationship between dissolved oxygen, lest temperature, load, and fluid is also discussed.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Rochester, New York, October 15–17, 1963.