Two isothermal (25 degrees C) phase diagrams with the block copolymer (EO)(43)(PO)(16)(EO)(43) and the block copolymer (EO)(5)(PO)(68)(EO)(5), respectively, in water and p-xylene are presented (EO is ethylene oxide and PO is propylene oxide). The copolymers have approximately the same molecular weight, albeit are unbalanced in PEO/PPO block ratio. The amounts and relative proportions of the solvents can modulate the resulting microstructures, although the phase sequence observed depends on the relative PEO/PPO block ratio. The copolymer rich in EO forms predominantly normal (oil-in-water) structures while the copolymer rich in PO forms predominantly reverse (water-in-oil) structures.