The present study is carried out in the context of a project whose primary aim is to define the physical components that could help explain what makes a syllable. We examine whether phonetic factors can account for observed universal trends in syllable structure, particularly those that provide an explanation for the Maximum Onset Principle (MOP). MOP forms the basis of syllabification theories allocating consonantal segments to syllable-initial position rather than to syllable-final position. Two theoretical frameworks can provide a phonetic basis for MOP, namely the Frame/Content Theory and Articulatory Phonology, but they do not account for it thoroughly. Consequently, we propose to reconsider the MOP in the light of new articulatory data focusing on basic jaw movements, and assume that MOP results from asymmetric jaw oscillation cycles. Kinematic data were obtained using a Carsten 2D Electromagnetic Articulograph (AG-200 EMA). Jaw oscillations were investigated for duration, velocity, amplitude of the opening vs closing phases, and then statistically analyzed according to different syllable structures. The results on French and Vietnamese bring out differences between the opening and closing phases, showing clear duration and velocity asymmetries. These results are, however, not consistent with previous works on American-English which can provide a phonetic explanation for MOP, based on the properties of the jaw cycles.