A test procedure was developed to assess the deposit-forming tendencies of gasoline/ethanol fuel blends, ranging from 0 % to 100 % ethanol (E0 to E100). The test engine was a Ford 1.8l - 4 cylinder -16 valve -natural aspirated flex fuel engine, which is used in various vehicle models, such as the European Focus and C-MAX.The test cycle, a realistic engine speed/torque profile, based on an urban driving pattern, provided good differentiation between different gasoline/ethanol fuel blends as well as between additized and non-additized fuel blends. With unadditized E85 critical deposits were found in the intake system, on the intake valves, in the combustion chamber and on the injector tips. Well known deposit control additives (DCA) used in gasoline such as PIBA (polyisobutyleneamine) and PEA (polyetheramine) were examined in E85 for deposit control effectiveness of intake valves, injectors and combustion chambers. The hump effect, known to occur in gasoline fuels at very low additive dosages, could not be found with this particular test engine and test cycle.The main cause of injector deposits with E85 fuel was identified to be engine design related.Going from E10 to E100 it was shown that higher ethanol contents tended to decrease intake valve and combustion chamber deposits, both with and without additives.Another test series simulated switching between E85 fuel and E5 fuel from one tank to another. This tanking pattern is relevant for markets were E85 and E5 (or E10) fuels are available at similar prices.The suitability of PIBA-containing additive packages for deposit control could be demonstrated for fuel blends up to 100 % ethanol content. For fuel blends of very high ethanol content, however, alternative additive packages were shown to provide improved compatibility with the fuel. An in-house filtration test permitted differentiation between conventional and new additive packages.