Hall coefficients and resistivities of a series of Bi2+xSr2−xCuOysingle crystals were measured to investigate the relation between the carrier concentration and the disorder of the system in the superconductor‐insulator transition. Excimer‐laser cutting technique was applied to fabricate the Hall‐bar shaped samples in order to determine precisely the transport properties of the single crystals. The Hall coefficients were found to be independent of the temperature, which suggests Coulomb interaction was negligible in the localized regime of Bi2+xSr2−xCuOy. We found the Ioffe–Legel conditionkFl∼1 laid aroundn0∼8×1020cm−3in this system, and the carriers in the localized regime were essentially ‘‘metallic.’’ ©1996 American Institute of Physics.