Gutmann acceptor numbers have been determined using P-31 nuclear magnetic resonance (NMR) for AlCl3/EMIC melts as well as LiCl, NaCl, and KCl neutral buffered melts. In AlCl3/EMIC melts, where EMIC is 1-ethyl-3-methylimidazolium chloride, the change in Gutmann acceptor number as a function of the AlCl3:EMIC melt ratio is attributed to an equilibrium between a monoadduct of triethylphosphine oxide . AlCl3 and a diadduct of triethylphosphine oxide . 2AlCl(3). Observed acceptor numbers for the neutral buffered melts appear linear with respect to the melt’s initial mole ratio of AlCl3:EMIC prior to buffering. The lithium cation appears to be the most Lewis acidic alkali metal cation followed by the sodium and potassium cations. Possible reasons for the change in acceptor number as a function of changing alkali metal cation concentration are presented.