Abstract Largely due to inadequacies of mapping software and complexities of data management, faults are traditionally treated as vertical planes for each separate reservoir zone or throughout the total reservoir within volumetric field models. This simplified approach results in errors in geometry and volume calculations. We discuss a software system which automates the volumetric modeling of multiple horizons exhibiting nonvertical faulting. The modeling is based upon the construction of fault plane grids from digitized fault traces and a set of attributes to describe the attitude of the fault. The fault plane grids are intersected with structural and isochore grids for each reservoir zone, producing a realistic set of migrated fault traces for each structural horizon. This greatly enhances the structural definition for volumetric analysis. Extensional fault models, incorporating normal, listric, and strike-slip faults can currently be built. The resulting horizon and fault grids may form the input for more advanced three-dimensional modeling software, providing a better structural framework. The Full Fault Modeling System (FFMS) is a stand-alone module. It has been designed to work closely with Radian’s CPS-3 Advanced Mapping Software, but can equally operate with any computer mapping package which uses rectangular grids. The FFMS software provides a structurally consistent approach to computer-based modeling of multiple surfaces affected by nonvertical faulting. The Ivanhoe field, situated in the Outer Moray Firth of the U.K. North Sea, has been used as a case history to demonstrate the application of the software and its methodology.