The concentration of metals in crankcase oils has been used for many years as an indication of the wear of various engine components. The technique has also been used to study the influence of other contaminants as well. In these respects this technique has been useful in avoiding expensive maintenance or in spotting unusual operating conditions. Industry guidelines have been developed which are considered to be indicative of dangerous concentration levels. These guidelines have in general neglected to consider the influence of oil consumption and oil additions on wear metals concentration. This paper treats these questions and shows that they can be quite significant in some circumstances. The paper also shows that wear metals concentrations can be used to establish wear rates.