This paper describes the results of an engine study of the tendency for fuel injector deposits to form by gasolines of various compositions. Since the factors promoting the formation of fuel injector deposits in DISI engines have, in many cases, been insufficiently identified they require further research and investigation work, which was the greatest motivation for undertaking this project. The latest CEC F-113-KC test procedure for the most damaging deposits in DISI engine injectors was used for this purpose. The research results obtained in the framework of the conducted project indicated T90, aromatic and olefinic hydrocarbons, sulphur, ethanol, DVPE, IBP and fuel density as the most important factors causing the increase in the tendency for deposits to form on the injectors of SI type DISI engines.