The addition of 7% FAME (Fatty Acid Methyl Ester) is mandated in a number of European countries since 2008. Higher FAME concentrations up to 30% are used by fleets in some countries. Passenger car manufacturers have reported on the negative technical implications of biodiesel on engine oil dilution, engine cleanliness and corrosion. The reason for the impact of FAME can be attributed to the higher boiling point compared to fossil fuel and the lower oxidation stability due to the presence of unsaturated fatty acid components.In this study engine oils with different performance level were evaluated in a taxi fleet test run with B5 and B20 biodiesel. The test results are illustrated with the used oil analyses and the performance of the engine oils by end-of-test engine inspections. The main conclusions from this taxi test are: B5 and B20 fuel affect piston cleanliness significantly depending on the engine type, deposits are formed with low levels of bio fuel concentration in the sump, and the reduction in piston cleanliness is comparable between B20 and B5.