Theoretical study of small methylaluminoxane sheets (MeAlO)n(Me3Al)m indicates that DFT electronically stabilizes those featuring 5-coordinate Al and 4-coordinate O compared with higher level MP2 and CCSD(T) calculations which favor 4coordinate Al. The anions formed from these precursors all feature 4-coordinate Al and their relative stabilities explain the appearance of ESI-MS spectra recorded during the hydrolysis of Me3Al.