Self-sustained vocal fold vibration is possible with either or both of two mechanisms: (1) a mucosal wave propagating along the medial surface of the vocal folds and (2) a vocal tract that offers inertive reactance. A quantitative comparison shows the mucosal wave mechanism has a lower threshold pressure and a higher glottal efficiency, but the supraglottal inertance mechanism can assist in the oscillation and is effective in optimizing the two mechanisms. It is concluded that optimal parameters are a mucosal wave velocity on the order of 1 m/s and a diameter of the larynx canal (epilarynx tube) on the order of 0.8 cm.