In Tierra del Fuego Province most of the hydrocarbons, usually gas with associated liquid, has been produced from the Springhill Fm., the typical and conventional clastic reservoir of the Austral Basin. The recent discovery of oil in reservoir levels of the Jurassic volcaniclastic Serie Tobífera in the Angostura halfgraben (San Martín Field) has encouraged the exploratory interest of this play in the area. Specifically, for the Argentine sector of Tierra del Fuego, this study addresses the first documented occurrence of oil with a geochemical pattern related to a lacustrine source rock in the Serie Tobífera interval of the AS.x-1001 (Angostura Sur) well, located southeast of the San Martin field. From chromatographic, isotopic and biomarker data, its origin is attributed to organic rich beds contained in the Jurassic halfgrabens of the Serie Tobífera. The Angostura Sur recovered oil can be clearly differentiated from other produced oils from the Serie Tobífera and the Springhill Fm. in the neighbor areas, which are largely dominated by Lower Cretaceous marine source rocks. These distinct genetic identities allow the recognition of two Petroleum Systems in the study area and delineate two end-member oil types. The latter are useful for interpreting the origin of other fluids characterized by intermediate patterns and mixed contributions. The generation capacity of the pre-Cretaceous lacustrine source rock of the Angostura halfgraben is discussed in terms of its analogy with Jurassic non-marine source rocks identified in the Pampa Palauco/Cajón de los Caballos area of the Neuquén Basin.