Biodiesel has gained more and more attention in recent years resulting from the fact that it is made of renewable resources. Parallel to its environmental compatibility, biodiesel also exhibits a high thermal stability. We demonstrate here that biodiesel can replace conventional oils as apolar phase in nonaq. microemulsions contg. the room temp. ionic liq. ethylammonium nitrate as polar phase. In addn. to the phase diagram and the viscosity of the microemulsions, we study the thermal stability of these systems. Along an exptl. path in the phase diagram, no phase change could be obsd. between 30 °C and 150 °C. Cond. measurements confirm the high thermal stability of these systems. The microemulsion exhibits a percolative behavior between 30 °C and 150 °C. Small angle X-ray scattering spectra show a single broad scattering peak similar to aq. microemulsions. The spectra could well be described by the Teubner-Strey model. Furthermore, the adaptability of different models ranging from bicontinuous structures to ionic liq. in oil spheres as well as disordered open connected cylinders has been checked. These high temp. stable, nonaq., free of crude oil based org. solvent microemulsions highlight an efficient way towards the formulation of environmentally compatible microemulsions and open a wide field of potential applications.