One of the primary functions of a lubricant is to preserve the cleanliness of a combustion engine's mechanical parts. The cleanliness of the mechanical parts is facilitated by the introduction of “detergency” and “dispersancy” additives to the engine oil. This last property, dispersancy, is the property that allows the oil to suspend and carry away “pollutants” of diverse sources, such as soot from combustion, metallic particles from wear, corrosion of mechanical parts, and insoluble products resulting from the aging of the oil, etc. Recently, with the arrival of new fuels (e.g., biodiesel, ethanol blends, etc.) we notice that the existing or traditional lubricants present an important variability in terms of durability and resistance to pollutants, such as the fuel or the biofuel. Our studies show that the dispersancy capacity of certain types of lubricants is significantly degraded by the presence of specific pollutants, and in particular fatty acid methyl esters of the biofuels, which have a significant impact. It is therefore important to quantify the degradation of the oil in-service (engines or transmission oils) and to monitor the evolution of the oil's dispersancy properties during use to be able to determine steps and intervals for maintenance. Additionally, for the development of new lubricants it is necessary to define a criterion of acceptance of the oil by its dispersancy capacity. This new method will define and quantify this criterion. The writers will present the results of these studies with particular emphasis on the impact of biofuels on the dispersancy capacity of both gasoline and diesel engine oils. They will describe a method of analysis using an automated instrument providing precise, objective measurement of this important parameter. This method will therefore be able to estimate the dispersancy capacity of lubricants, as well as the implication of various pollutants on this parameter.