An integrated study of the South Gabon Margin (South Atlantic) based on reflection seismic and well data has been performed to quantify tectonic activity. A regional profile crossing the entire basin together with subsidence analysis, highlights important aspects of the post-rift history. The most striking event in the margin evolution appears to be the anomalous extra subsidence during the early post-rift period characterized by high sedimentation rates, equivalent to one third of the syn-rift subsidence. Although the presence of evaporite layers restricts knowledge of the underlying structures essentially composed of pre-rift and syn-rift sequences, the outcome of this post-rift tectonic study has strong implications for the rifting history. The early post-rift subsidence patterns can be related to a high thermal anomaly during the early rifting thermal state of the lithosphere. These findings are highly relevant for petroleum system studies and have implications for hydrocarbon generation.