Three oxyethylene/oxybutylene triblock copolymers of similar E-block length but different B-block lengths (B4E40B4, B5E39B5, and B7E40B7) were prepared by sequential anionic polymerization and characterized by gel permeation chromatography and NMR spectroscopy. Their association in aqueous solution was investigated by static and dynamic light scattering, and evidence was found for small molecular associates, micelles, and micelle clusters (bridged micelles). Values of the critical micelle concentrations and micellar association numbers were determined and compared with those for related diblock (EmBn) and triblock (EmBnEm) copolymers.