Small-angle neutron scattering was used to characterize the length scales and interfacial properties of water-alkyl ethylene glycol ethers (CkOC2OCk)-n-alkyl polyglucoside (CmGn) bicontinuous microemulsions systematically as a function of surfactant structure and oil hydrophobicity. Analysis of the scattering spectra in terms of a thermodynamic model shows that on approach to the tricritical point in water-CkOC2OCk-C8βG 1-NaClO4 mixtures the solution microstructure dissolves. With increasing alkyl chain length of the surfactant (m), water-CkOC2OCk-CmGn mixtures become increasingly structured. Conversely, increasing the surfactant headgroup length (n) makes the mixtures slightly less structured. The variations in solution microstructure with changes in m and n are not as large as those observed with changing surfactant structure in water-alkane-CiEj mixtures. Exchanging the α-D (CmαG1) for β-D (CmβG1) form reduces the degree of correlation between the water and oil domains in water-CkOC2OCk-CmG1 mixtures. Increasing the alkyl chain length of the oil (k) produces increased structure in all mixtures studied, which is in contrast to the trend observed in water-alkane-CiEj mixtures. Analysis of the Porod regime of the scattering spectra of several water-CkOC2OCk-CmG1 mixtures shows that the average headgroup area of the CmG1 surfactants increases as the oil hydrophobicity (k) decreases. The increased surfactant headgroup area presumably results from increased oil solubility in water, which in turn allows for more contact between the oil and water at the interface and a larger distance between CmG1 molecules.