Seismic images are extensively used by petroleum geologists to delineate subsurface geological structures. This interpretation is dependent on interpreter's individual skills, and expertise causing a complex seismic image to be interpreted differently by different seismologists. To overcome this uncertainty a prototype expert system SeisExpert, has been developed in which the experience and heuristic knowledge of the experts have been incorporated in the form of a set of rules. Over 120 rules have been built into a commercially available expert system shell, ‘Flex’ (from Logic Programming Associates, UK). Information received from the user is chained through these rules to interpret the seismic images. Additionally, analytical procedures have been provided to refine the interpretation in case of complex subsurface structures. These include statistical cross-correlation across the seismic traces and secondary attributes such as instantaneous phase and reflection strength. Using this system, several horizons were successfully tracked across seismic traces in seismic images containing field data from existing oil fields. Discontinuities such as faults, were also identified.