Data on oil reserves in the Niger Delta basin show a bimodal lognormal distribution with the break in slope reflecting variation in exploration maturity, quality of prospect, and distribution of giant oil fields.

Several areas of anomalous reserves are defined by the selected threshold oil-reserves density of 200,000 bbl/km². Five major prolific centers (with reserves contrast > 3) are aligned in an arcuate belt (prolific belt) which is an image of the present coastline.

The prolific belt marks the transition zone between oceanic and continental crusts, a zone of weakness characterized by increased tectonic activity. During passage through the belt, the Niger Delta system was predominantly constructive and consisted of at least five delta complexes which now define the prolific centers. Beyond the prolific belt, predominance of destructive processes resulted in merging of the delta complexes. In these areas, the distribution of zones of major concentration of reserves developed in response to alternate channel switching and extension superimposed on growth-fault activity.

The prolific belt and offshore zone coincide with a hot geothermal belt that frames a geothermal minimum at the delta center. The coincidence, together with the progressively younger sediments from north to south, suggests that the maturity per unit depth is less in the offshore zone and central delta nose than in the prolific belt. Implied are deeper levels of hydrocarbon occurrence as well as a lesser amount of generated hydrocarbons offshore and on the central delta nose than in the prolific belt. These factors and the relatively shallow depth of investigation probably account for the present absence of prolific centers south of the prolific belt.