The goal of this research is to examine acute effects of oil on reefs and reef communities on the northern Gulf of Mexico (Gulf) continental shelf. We will examine reef fish community structure and live-bottom habitat via analysis of video collected during transect sampling with a remotely operated vehicle (ROV), as well as directly sample fish for various tissue analyses. A large pre-spill data set will permit statistical tests of oil effects on taxa-specific density and measures of community structure. Assays of fish liver tissue and bile will serve as measures of petroleum exposure, while the effect of exposure will be inferred from differences in fish condition (bioelectrical impedance and mass-length relationships) and size-at-age between pre- and post-oil time periods, or between populations in contaminate versus uncontaminated regions of the Gulf. Results of this study will provide estimates of acute effects of oil exposure on reefs and reed fishes that are imperative for the ongoing Natural Resource Damage Assessment (NRDA) ecosystem injury assessment process as specified under the Oil Pollution Act of 1990. Furthermore, results of this study will serve as a critical precursor for later assessments of chronic effects of oil on reef habitats and communities.