Dispersancy is calculated based on the different diameters of the annular black deposits on the dot. It is given as a value between 20 and 100. A value of 100 represents a fresh oil. The lower the dirt carrying capacity value, the less the oil's additive package is able to carry soot and dirt. A value lower than 30 indicates that the oil does not prevent deposits in the engine.

Dispersants are the indispensable counterpart to detergents. They keep the detached contaminants in suspension and ensure that they cannot form new deposits. In doing so, they literally envelop the dirt particles and enable them to be transported to the filter.