The phase behavior of an oxyethylene/oxybutylene diblock copolymer (E22B7) in aqueous solution was defined using three properties: yield stress (by rheometry and tube inversion), dynamic modulus (by rheometry), and structure (by small-angle X-ray scattering). The boundary of immobile, structured gel (hard gel) was detected by all three methods, giving satisfactory agreement. A structural transition within the hard gel, from bcc to hex, was detected by rheometry and SAXS. Two types of soft gel were detected and assigned to disordered phases containing either spherical or cylindrical micelles. Comparison with results for other diblock EmBn copolymers showed a regularity of behavior influenced largely by oxyethylene-block length, with oxybutyleneblock length having a minor but significant role.