Boron trifluoride clusters are formed in a supersonic expansion and ionized by electron impact. The resulting ion distribution is analyzed by time-of-flight mass spectrometry. The only consistently observed, extended series of peaks in EI of BF3 clusters is BnF3n-1+. Ab initio modeling of these ions informs our speculation regarding their internal structure and ion-molecule chemistry involved in their formation. Formation of B2F5delta+ is computationally predicted to occur in all of the cluster ions we observe (n = 2-8) except B3F8+. BF4delta- units are evident in the predicted structure of B8F23+.