Drop-shape techniques, such as axisymmetric drop-shape analysis (ADSA), have been widely used to measure surface tension. In the current schemes, theoretical curves are fitted to the experimental profiles by adjusting the value of surface tension. The best match between theoretical and experimental profiles identifies the surface tension of the drop. Extracting the experimental drop profile using edge detection, is an important part of the current drop-shape techniques. However, edge detections fail when acquisition of sharp images is not possible due to experimental or optical limitations. A new drop-shape approach is presented, which eliminates the need for the edge detection and provides a wider range of applicability. The new methodology, called theoretical image fitting analysis (TIFA), generates theoretical images of the drop and forms an error function that describes the pixel-by-pixel deviation of the theoretical image from the experimental one. Taking surface tension as an adjustable parameter, TIFA minimizes the error function, i.e. fits the theoretical image to the experimental one. The validity of the new methodology is examined by comparing the results with those of ADSA. Using the new methodology it is finally possible to enhance the study of the surface tension of lung surfactants at higher concentrations. Due to the opaqueness of the solution, such studies were limited to the low concentrations of surfactants heretofore. (C) 2004 Elsevier B.V. All rights reserved.