In order to increase the solubility of ethanol in diesel, it is necessary to introduce an additive which improves the solubility in a more stable way, especially in low temperatures and when exposed to the air humidity. Theses additives, which function is to stop the phase separation, act as cosolvents in ethanol-diesel blends. In the present work, the authors present the physical and chemical principles under which the cosolvent material acts. Additionally, they propose and evaluate the additives SPAN80 and AEP-102 as promoters of the blends of diesel fuel with 8% anhydrous ethanol, determinating quantitatively the concentration of water admissible.