Oil and gas seeps associated with petroleum-producing regions commonly occur in the Gulf of Mexico. Total scanning fluorescence and capillary gas chromatography using both flame ionization, flame photometric, and mass spectrometric detection have been used to detect the presence of upward-migrated aliphatic, aromatic, and sulfur-containing compounds in near-surface sediments. delta/sup 13/C-CaCO/sub 3/ has also been used to detect the formation of authigenic carbonate associated with hydrocarbon seeps. These measurements can at least be used to delineate regional trends of oil-prone areas versus gas-prone or dry areas. Evidence from individual productive blocks associated with hydrocarbon seep anomalies is also presented, suggesting a finer scale for these measurements. Data to be presented include: (1) broad regional trends in hydrocarbon seeps on the Gulf of Mexico continental shelf, (2) vertical trends of migrated hydrocarbon in boreholes over productive blocks, (3) molecular and isotopic correlation of surface bitumens with reservoired oil, and (4) delta/sup 13/C-CaCO/sub 3/ trends associated with seeps in the Green Canyon area. Sampling and replication requirements for reliable offshore surveys will be discussed.
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