The utility of micropalaeontology and biostratigraphy has perhaps been nowhere better demonstrated than in the Gulf Coast of the United States. Gulf Coast micropalaeontology and biostratigraphy evolved through several phases in response to the shift in exploration from onshore to the deep Gulf of Mexico. During this time, micropalaeontology and biostratigraphy morphed into the discipline of chronostratigraphy while playing critical roles in exploration due to the complex geometries produced by the interplay of sea-level change, shifting loci of sedimentation and diapirism. Micropalaeontology, biostratigraphy and their latest incarnation of chronostratigraphy have contributed to the discovery, exploration and development of new fields and trends while saving countless hundreds of millions, if not billions, of dollars in exploration and development costs, as well as significantly adding to reserves by discovering new reservoirs that would otherwise be missed by the drill. Chronostratigraphy will continue to play a critical role in the exploration and development of the latest Gulf of Mexico frontier play: the Lower Tertiary Deepwater Wilcox Trend.