Upper Triassic (Rhaetic), thick, argillaceous deposits are the source of important Italian hydrocarbon accumulations. This study integrates sedimentology, paleoecology, and both organic and inorganic geochemistry to determine the genesis and source potential of these marine deposits, which are ascribed to two depositional sequences. The first Rhaetic transgression was associated with an interruption of carbonate production and with a strong increase in the preservation of organic carbon. Deposition of these sequences was controlled by interactions between carbonate and terrigenous sediment sources, under the influence of high-frequency eustatic fluctuations. Most of these organic-rich Rhaetic successions are presently overmature and appear to have entered the oil window d ring Mesozoic time, prior to trap-forming tectonics. Important exceptions are represented by Mesozoic paleohigh areas, where Triassic deposits reached maturity in the Neogene, or are still immature.