High resolution biostratigraphic analyses provide calibration of both depositional systems and specific depositional environments. Such studies facilitate prediction of reservoir geometry and the lateral continuity of both reservoir sandstones and sealing shales. Data from the offshore Nigeria Oso Field is presented as a case study of one late Miocene deltaic depositional system. Within the Oso Field, marine shales are recognized as effective topseals across the entire field in contrast to marginal marine to nonmarine shales which have more restricted distribution and act as intrafield baffles. Multiple sequence stratigraphic models have been considered; one model based on regional seismic and well-logs data, one on log-motif and core sedimentology, and one on biostratigraphic data integrated with core sedimentology. The lower Oso Field producing interval is interpreted as a lowstand prograding wedge and the upper interval as a prograding distal transgressive or alternatively distal highstand system tract, based on integrating all these data.