Abstract: Process and apparatus for analyzing the characteristics of a liquid/fluid interface, especially in the presence of surface-active agents. A tensiometer operates according to the principle of the suspended drop and the amount of liquid injected in the drop is adjusted according to the value of the calculated interface tension; the volume of the formed drop is progressively increased as the interface tension tends to diminish. A drop-forming device (30) can acquire an image of the drop and read the drop contour (40), can calculate the interface tension based on the shape and the size of the contour, and can adjust the same. A method of high speed measurement of interface tension uses all the points in the drop contour and provides a value in less than a second with the aid of a microcomputer.