Two isothermal (25° 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.