A technique for measuring the evolution of tube shape in terms of cross-sectional area as a function of both time and axial position during the course of self-excited oscillation is described. The conductance catheter method is used to measure instantaneous shapeindependent area at incrementally adjusted positions along the length of the tube. Pressure at the downstream end of the tube is also recorded, and this signal is subsequently used to line up all the area recordings. The result is a surface of cross-sectional area versus position and time that shows explicitly how disturbances propagate along the tube, the localization of the oscillations to the downstream end, and the shape signature of a given mode of oscillation. Derived results include profiles of the oscillation maximum, minimum and amplitude along the tube, and the time-course of movement of the area minimum (the tube throat) during the cycle. Similar procedures have been used in conjunction with a fine pressure-transducing catheter to obtain pressure surfaces. The technique is limited to strictly periodic oscillations, and to this end the extent of periodicity of operating points representing different combinations of controlling parameters has been systematically investigated. Three different modes of oscillation of a single collapsible tube have been observed with these techniques. These modes have previously been shown to be distinct, with sharp transitions separating them. Two of the modes have a similar low frequency, and are distinguished by waveform shape: the collapse is either brief relative to cycle length or lasts for approximately half the period. The third mode has approximately three times the frequency of the other two. On the basis that the higher-frequency mode is obtained by transition from the brief-collapse mode as the appropriate parameter is varied, it was previously postulated that these two were more closely related dynamically, and the detailed examination of waveforms here confirms this link.