Potential energy profiles have been determined for the two series of reactions : (i) X(-) + HCOY, where X = Y = H, F, or Cl, and (ii) X(-) + RCOX, where X = F or Cl and R = SiH3, CH3, H, CN, or NO2. Energies of all stationary points, including reactants, ion-dipole complexes, stable adducts, transition states, and products, were evaluated at the Hartree-Fock (HF) and the second-order Moller-Plesset (MP2) correlation levels with the 6-311++G** for reaction series i and with the 6-31+G* basis set for reaction series ii. The results predict that acyl-transfer reactions can proceed through single-well, double-well, and triple-well energy profiles in the gas phase depending on the nucleophile, X(-), nucleofuge Y-, and acyl group R. Factors that favor the single-well or triple-well profile with a stable tetrahedral adduct are (a) stronger bond formation of the C-X or C-Y bond, (b) stronger nucleophilicity of X(-) and poorer leaving ability of the nucleofuge, Y-, (c) wide energy gap between the two antibonding MOs, pi*(C=O) and sigma*(C-X), and (d) strong electron acceptor acyl group, R. Whenever gas-phase experimental results are available, good agreements were obtained with our MP2 predictions.