Bowel sounds have been speculated to stem from the movement of gas or a mixture in the bowel lumen, with gas as the major component. The exact role and the mechanism through which gas participates have not been elucidated. Video images of actively moving bubbles under either real-time ultrasonography (RU, n = 4) or videofluoroscopy (VF, n = 4) with synchronous sound recording were studied and a total of 24 bubbling bowel sounds (BBS's) were obtained. The physical dimensions and acoustic parameters of bubbles were analyzed. Freely oscillating bubbles were demonstrated clearly in both groups. Bubble radii ranged from 1.5 to 7.2 mm and frequencies from 258.3 to 1,078 Hz. The bubble frequency correlated inversely with the radius (P < 0.01). The relevant acoustic features and parameters of bubble dynamics further supported the identification of gas bubbles. Although the acoustic features seemed to be of minor clinical significance, increased number of clustering or fixed, repetitive pattern of occurrences might suggest a poorer prognosis. In summary, oscillating gas bubbles are capable of producing BBS's and may play a central role in this newly recognized model of bowel sound genesis. The patterns of BBS's may be of prognostic value in clinical application, underlining the need for further study.