Abstract The ARI* Azimuthal Resistivity Imager is a standard laterolog equipped with an additional segmented electrode. This segmented electrode provides twelve deep calibrated azimuthal resistivity measurements. As any electrical device, the ARI tool is sensitive to fractures filled with conductive fluid. Finite-element modeling was performed to study the tool response to fractures. It shows that techniques similar to those used to characterize fractures with the FMI* Fullbore Formation Microlmagcr can be used with the ARI tool. But it also demonstrates that the extension of the fracture (or the length of mud invasion for an oil filled fracture) and its width (aperture) are equally important parameters when characterizing the fracture. From the resistivity image, the geometry of the fracture (dip and azimuth) can be computed. A lower limit of the fracture aperture and a lower limit of the fracture extension can be estimated from the azimuthal resistivities. Log examples illustrate the proposed technique.