Pozo D-129 Formation Paleogeographic model. Its application to reserves development in Golfo San Jorge Basin, Argentina A regional paleogeographic model for the upper section of the Pozo D-129 Fm based on the interpretation of 2D/3D seismic data, well logs and rock samples was generated. Detailed characterization of this model in the Cerro Dragón area led to the discovery of gas reservoirs which have produced 254,7 bcf of gas (7.212 x 106 m3) and have proven reserves as of Dec-13 of 332,0 bcf (9.402 x 106 m3) of gas. This has set the Cuenca del Golfo San Jorge as the third gas productive basin in Argentina. Detailed interpretation of isopach time maps, analysis of seismic attributes and character of the seismic data together with the paleoenvironmental interpretation from well information allowed the identification of proximal shelf, slope and distal lake deposits. Thicker fan-shaped slope deposits are where reservoirs develop. Reservoirs are seismically characterized by high amplitude, low acoustic impedance and with Type IV AVO and in logs by high GR, high effective porosity -up to 30%- and where VP/VS ratio distinguishes between gas and water zones. Wells drilled in these thicker sections showed a succession of amalgamated tuffaceous sandstones, sandy tuffs and tuffs in a 25 to 30 m upward increasing porosity arrangement repeated up to 4 times and separated by very fine tuffs with ostracods. These deposits are interpreted as the aggradation of dilute flows bringing sediments in from the shelf. Traps are structural - Tres Picos D-129, Valle Martín D-129 and Coirón Fields - or stratigraphic - Trahuil Field - with vertical seal being the basal section of the Mina del Carmen Fm and lateral seal low permeability background facies of the Pozo D-129 Fm.