An hypothesis of the mechanism of the formation and growth of deposits from jet-engine lubricants in today's jet engines is discussed. Deposit formations are most often found in areas of the engines which are not flood-lubricated. Lubricant is transported as a spray or mist to hot static areas of the engine where deposits can form. The “Oil Mist Deposits Test,” a laboratory technique which can be used to differentiate between the deposit-forming tendencies of lubricants, is presented. The results obtained by the laboratory technique are equated to levels of deposits found in field engines.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Minneapolis, Minnesota, October 18–20, 1966.