A spatial exposure analysis program was designed to quantify, display and compare the impacts of potential oil spills on estuarine ecosystems. The program integrated GIS and the output of an oil spill transport and fate model to summarize temporal contam inant exposure over geographical space. Two approaches were developed and compared: one based entirely on ARC/INFO (ESRI, 1994) macro commands and the other based on a combination of a program written in C language and ARC/INFO commands. In the first a pproach simulated oil spill output from the transport and fate model was converted and processed, completely within ARC/INFO, to calculate spatially explicit exposure over time. The results were then used for overlay analysis with offshore resource cover ages. The C program developed for the second approach was used to save computation time during intensive calculations of exposure. Both vector and grid representations were used in this development. Tampa Bay, Florida, is used as a case study.