Tierra del Fuego Island, in the Austral Basin. The exploitation license was given by the "Secretaría de Energía" without the compromise of an exploration well, based on geological and geophysical studies documented by the interpretation of nearby wells outside the Leo zone, 2D seismic lines covering the block and analogies with other fields operated by Total Austral in Austral Basin. Leo field is a pioneer case of exploitation concession awarded before the drilling of an exploration well due to DHI (Direct Hydrocarbon Indicators) and the comparison with analogue fields. The sands which make up the reservoir of the Springhill Formation correspond to the Argo sequence and have been deposited in a marine environment on the paleo relief of the basement and/or the Serie Tobífera. The lithological and petroelastic properties have been used to characterize and delimit the gas accumulation within the structure. The AVO effect (amplitude variation with off-set) is the seismic consequence of this kind of reservoirs: high porosity, low impedance gas bearing sandstones. Such effect is very common in the Austral Basin. Three reservoir models were built after bringing together the geological information of wells close to the structure and the interpretation of several attributes based on the 2D seismic. The three models include the most likely one and two more models taking into accounts uncertainties. The purpose of such construction was to quantify the gas accumulation, to assess the risks and to be used as the basis for the proposal of a well. Leo x-1 was drilled on the apex of the structure and it confirmed the presence of gas and the quality and productivity of the reservoir. The discovery well was drilled in 2015 with its completeset of conventional logs, CRM, an 18-metre core, laboratory studies and multimineral interpretation of logs. An extended dynamic production test (DST) proved a minimum connected volume which was enough to finish the exploration and appreciation stages, and to prepare the development based on a horizontal well. Finally, three additional models have been built based on the information acquired by the well. The quality control has been performed by means of a dynamic simulator and the creation of 2D synthetic seismic lines from the 1P, 2P and 3P static models, based on the parameterization of properties of the reservoir model.