The phase diagrams of systems composed of polyoxyethylated non-ionic surfactants/ water/dodecane/pentanol were studied as a function of the oxyethylene chain length. The region of existence of the microemulsions was optimized for a surfactant containing ten oxyethylene units per molecule. The influence of the surfactant to cosurfactant ratio is investigated. The low interfacial tensions produced by these non-ionic emulsifiers demonstrate an efficiency comparable to that of ionic emulsifiers. -- AATA