The airgap harmonic frequencies of a single-phase squirrel-cage induction motor are studied analytically using the permeance method. This approach delivers detailed information about the airgap harmonic frequencies, corresponding pole-pairs, and the originating mechanism such as excitation, slotting, or saturation. In order to verify this analysis, experimental measurements are carried out on a 1/3-hp single-phase induction machine. The harmonic frequencies and nature of field waveforms are studied at different operating conditions. Excellent correlation is found between theoretical and experimental results. Finally, the usefulness of these results is outlined.