Mixtures of n-decyl beta-D-gluco-pyranoside (C(10)G(1)) and n-nonyl beta-D-gluco-pyranoside (C(9)G(1)) in water were studied to determine the location of a closed-loop liquid/liquid miscibility gap. A phase diagram including the point at which the closed loop first appeared was determined, as well as the effect of salts on the location of the consolute boundaries of the loop. The microstructure surrounding the miscibility gap was investigated using time-resolved fluorescence quenching, cryo-trans mission electron spectroscopy, and self-diffusion NMR. There appear to be bicontinuous structures of interconnected rods on both sides of the miscibility gap, with evidence for more extensive networks in the concentrated micellar and higher temperature regions surrounding the closed-loop miscibility gap.