Water accumulated in motor oils in the process of use exercises a profound effect on the fundamental properties of the oils: lubrication efficiency of the oils chan ges and their tendency for sliming increases. It is commonly believed that precursors of slime are products of nitration or sulfonation of aromatic components of fuel fractions. However, Russian scientists proposed a different concept of the mechanism of low-temperature sediment formation (sliming): products of thermolysis of heavy aromatic hydrocarbons, viz., asphaltenes, which possess paramagnetic properties, play the decisive role in this process. Indeed, these products, by reacting with water, form a "soft precipitate."