The phase behavior of mixtures of water, octane, n-alkyl polyglycol ethers (C(i)E(j)), and n-alkyl beta-D-glucopyranosides (C(m)G(1)) is systematically studied as a function of temperature and composition, The addition of C(m)G(1) to water-octane-C(i)E(j) mixtures promotes formation of a three-phase region that is nearly independent of temperature in all mixtures studied. The size and extent of this three-phase region are shown as a function of C(m)G(1) concentration and hydrophobicity and C(i)E(j) amphiphilicity. This unique behavior arises from the extremely low oil solubility of the alkyl monoglucosides.