The association properties of block copolymer E18B10 in aqueous solution have been studied. We use E to denote an oxyethylene unit and B an oxybutylene unit and m and n to denote block lengths in chain units. The samples had E blocks terminated by methoxy groups but B blocks terminated either with hydroxy or with methoxy groups. Surface tensiometry was used to determine the critical micelle concentrations of the samples at several temperatures and thereby values of the enthalpy of micellization. Dilute solution viscometry was used to investigate the geometry of micelles in solution. Critical micelle temperatures were found to be insensitive to the B-block end group and to the geometry of the micelles, whether spherical or wormlike.