The application of a fast imaging technique to dipole-dipole resistivity data from the Ahuachapan-Chipilapa geothermal field produces resistivity sections comparable to those obtained by trial-and-error methods using relatively intensive forward computations. The imaging technique is an approximate inverse method based on low resistivity variations that produces reasonably good results for moderate and high resistivity contrasts. The method considers distributions of minimum structure for representing the earth and uses quadratic programming in the search for acceptable solutions. The images are obtained in a single iteration in the fashion of a fast transformation of apparent resistivity pseudo-sections into true sections of resistivity versus depth. The transformation was applied to four long-offset dipole-dipole lines. The same lines were also interpreted independently using exact forward modelling by different interpreters. In general, the images reproduce the main features of the forward models but also include subtle variations that are difficult to recognize in trial-and-error results. In some cases, the images combine features of the different individual models obtained by the interpreters. The application to Ahuachapan-Chipilapa illustrates the usefulness of the imaging technique in the interpretation of dipole-dipole resistivity survey data from geothermal fields.