Abstract Although some unpublished planktonic foraminiferal zonations were being used for onshore subsurface Wilcox correlation prior to 1994, Rosen et al. (1994) was one of the first publications suggesting a tested zonation and relating it to relative changes of coastal onlap. Since 1994, hundreds of additional wells have been analyzed, resulting in the refinement of the zonation and a better understanding of the depositional environment. A refined early Eocene to basal Paleocene zonation for subsurface Reklaw–Wilcox–Midway formations, based on 21 planktonic and 24 benthonic foraminiferal datum markers, has been established. Their correlation to global planktonic P -Zones as well as the local benthonic foraminiferal zones is given. The environment in which they were deposited and their relation to 13 condensed sections, as related to maximum flooding surfaces and system tract boundaries in subsurface Texas and Louisiana, are discussed. Their similarities and differences with the recent ultra-deep water Wilcox discoveries are compared. This zonation is based on analysis of more than 600 wells, construction of several regional environmental maps, and integration with electric logs and 2,500 miles of high-resolution seismic data, in the Wilcox trend, south Texas to central Louisiana.