A homologous series of branched, non-ionic surfactants with the general formula CnG(EmM)2, where Cndenotes an alkyl chain, G = glycerol and EmM = oligo-oxyethylene mono-methyl ether, has been prepared from alkyl bromides (n= 10–16) and several monodisperse 1,3-di(methoxyoligo-oxyethylene) ethers of glycerol (m= 3–5). The branched hydrophilic chain is introduced to modify the interfacial area compared to corresponding linear oligo-oxyethylene surfactants (I-amphiphiles) without essentially changing the hydrophilic-lipophilic balance. The phase behaviour of these Y-surfactants in aqueous solution reveals that according to established packing models the branched hydrophilic group strongly stabilizes the cubic and hexagonal mesophases, while a lamellar phase is not observed.