The paper deals with the problem scope of ethanol (as biologically decomposable compound) adding into petrol and diesel fuel on the final lubricity of motor fuels. It analyses the subject of tribology and automobile fuels in connection with modern technologies in construction of automobile engines. The mentioned properties and characteristics were measured by commonly used laboratory method on Plint TE 82 (PLINT & PARTNERS LTD). Measured data show, that diesel fuel with ethanol has better lubricity parameters and lubricity persists longer, than in case of petrol fuel with ethanol. One problem occurred, when diesel fuel was mixed with ethanol, which contained more then 0,5 % of water. This problem was solved by eliminating of the water from ethanol, eventually the suitable solubility additive is recommended.