The Gulf of Guinea continental margin is paralleled by a coastal relief that isolates the Congo drainage basin and can play a subsequent role in interactions between margin deposits and continental denudation: Migration of depocenters from the Ogooe and Kwanza Rivers to the Congo fan in the Oligocene, low present-day sediment delivery, or Pleistocene submarine channels instabilities are possible evidences for this interaction. In order to test this hypothesis, we examine successively margin isostasy, regional uplift, erosional unloading and flexural bulge created by sediment loads. Satellite free air gravity and two-dimensional thermomechanical modeling, including depth of necking, are used to determine the structure of continental margin and strength conditions for two selected sections across South Gabon and Congo fan. Both verify similar conditions for extension geometry, depth of necking (10--20 km) and strength (equivalent elastic thickness of 20--30 km); differences in observed gravity are explained mainly by differences in sediment volumes. Regional uplift during Miocene of at least 450 m is attributed for both continent and margin, as evidenced by the elevated base level of the Congo drainage basin and the uplift of shelf break and coastal plains. Topography corrected for regional uplift, valley erosion below relics surfaces, and corresponding erosion unloading has been determined as a proxy of Oligocene topography; it shows a typical rift shoulder topography isolating Congo drainage basin from margin. In such conditions, small-amplitude flexural uplift related to sediment loads can possibly have negative feedbacks for both Oligocene and present time.