The living oligomerization of isobutylene initiated by cumyl chloride 1 or by the telechelics P1 or P2 in presence of BCl3 and benzyltriethylammonium tetrachloroborate has been investigated. The tertiary chlorides P2-P7 were separated by HPLC and analyzed as spectroscopically pure compounds. A kinetic model has been derived from which the gross propagation rate constants for the early propagation steps can be calculated. It has been found that the low reactivity of the adduct of cumyl chloride to one isobutylene unit (Pi) is responsible for the broad MWD in the cumyl chloride/BCl3/BCl4--initiated oligomerization of isobutylene. In contrast, a narrow MWD could be achieved by using the 2:1 product P2 in combination with BCl3/BCl4- as initiator.