The deep part of the Gulf of Mexico basin, which is underlain by oceanic crust, has generally been regarded as a tectonically stable part of the basin since its formation by sea-floor spreading and thermal subsidence during the Late Jurassic-Early Cretaceous. Subsequent subsidence is believed to have been caused mainly by thermal cooling and sediment loading. A backstripping study, however, has revealed a tectonic event in the western deep basin with tectonic-loading effect today. One possible explanation is Laramide fold-thrust loading along the western flank of the basin during ∼66-40 Ma.