The simple extensional model for the subsidence of the northern United States Atlantic continental margin attributes subsidence, which results in sedimentary-basin formation, to extension and thinning of continental lithosphere. The model is used to predict the tectonic subsidence histories that would be associated with various amounts of extension. Actual tectonic subsidence history curves are calculated from data collected in the Continental Offshore Stratigraphic Test (COST) wells B-2, B-3, G-1, and G-2 and are found to be consistent with the predictions.