The Niger delta is a huge depocenter which slowly prograded seaward at a rate of 5 km/m.y. for at least 40 m.y. accumulating tens of thousands of feet of sediments. Presumably, for depocenters of this size, the depression of the lithosphere caused by sediment loading should extend beyond the point to which sediments can spread. To what degree will sediments be able to infill this theoretical depressed area? For the Niger delta, the distribution of most producing oil fields and the vertical sequence of sediments suggest a simple infilling mechanism. The peripheral moat which should surround the depocenter seems to be marked on the landward side of the tidal flats by two reentrants, one on either side of the delta. During the formation of the delta, this reentrant seems to ave induced, from time to time, major shifts of the Niger River which are recorded in the geologic section as a major transgression (or as a major regression on the opposite reentrant). The shifts seem like those of a pendulum, as suggested by the distribution of the transgressive shales which cap the producing oil fields. They provide a possible explanation for the distribution of the prolific belt and its prolific circles.