The potential energy surfaces corresponding to the Beckmann rearrangement (BR) of a series of aliphatic and cyclic alkanone oximes have been explored using density functional theory (DFT). In order to probe the reactivity of cyclohexanone oxime, the basic component in the industrial production of nylon-6, different model compounds were examined including formaldehyde oxime, acetone oxime, cyclopropanone oxime, cyclobutanone oxime, cyclopentanone oxime and cyclohexanone oxime itself. Geometries and energies were calculated using the B3LYP functionals in conjunction with the 6-31G(d,p) basis set. The influence of alkyl substitution in both aliphatic and cyclic forms on the simplest gas phase systems does not change the reaction pattern of the unsubstituted species and suggests that the most favored path remains as follows: protonation of oxime --> N-protonated species --> 1,2-H-shift --> O-protonated species --> migration-elimination --> fragmentation products, in which the 1,2-H-shift connecting both protonated isomers is rate-determining While methyl substituents on C of the oxime have only a small effect on the rate-controlling energy barrier, they significantly modify the fragmentation barrier. A similar trend occurs when ring structures are considered. Overall, it is confirmed that the difficulty, if any, in converting an alkanone oxime to BR product resides in the formation of its O-protonated form, indirectly from the more stable N-protonated form, rather than in the conversion of the O-protonated form into its products.