The Gulf of Mexico is a mature hydrocarbon basin, but one where new plays have continued to extend the hydrocarbon prospectivity beyond what was originally thought possible. The deepwater play, for example, resulted from challenges to a paradigm that limited the transport of reservoir-quality sand to large distances offshore. Since the initial deepwater discoveries, tests in ever-deeper water have regularly occurred. Deepwater discoveries occurred first in the Pliocene and the Miocene and more recently in the Paleogene. In 1999, deepwater oil production surpassed oil production from the shelf and increased total production in the Gulf of Mexico by more than 60%. Additionally, a deep shelf gas play has emerged due to a better understanding of concepts affecting gas formation and porosity preservation in high-temperature and high-pressure reservoirs.