The Gulf of Mexico is an active basin with complex geology, recent world-class discoveries ( Offshore , September 1999), and considerable business activity, including partnering, acquisition, and divestiture. More than 150 companies are active in the Gulf, each with its own philosophy and each at various stages in the exploration-production cycle. As a result of this activity, a wide variety of public domain, commercial, and proprietary data exists about the Gulf of Mexico. In fact, so much work has been done and documented that it is difficult to be aware of all available information, let alone analyze it and use it to make technical and managerial decisions. Clearly, a comprehensive GIS database that incorporates cultural, geologic-geophysical, engineering, infrastructure, and business-related data can allow a company to analyze the different data types more effectively and gain insights that are not otherwise apparent. This article illustrates applications of GIS technology in the Gulf of Mexico using a database that has been built and refined over three years. The software that we use, ESRI's ArcView GIS, runs on a PC and is commercially available. We define seven phases of oil company activity and identify the types of questions that are important at each phase. We then illustrate how a GIS database can help geoscientists, engineers, and managers to answer those questions, using examples from different parts of the Gulf (Figure 1). We have intentionally kept text to a minimum in order to let the figures tell the story. Figure 1. Index map shows location of the maps in this paper. Onshore surface geology from USGS. All maps are projected with following parameters: Lambert Conformal Conic projection; Clarke 1866 spheroid; Central Meridian, 98.005 W; Standard Parallel 1, 24.0°N; and Standard Parallel 2, 29.9°N. When deciding whether to enter a new basin, a company needs to understand the …