Exploration in the offshore Golfo San Jorge Basin requires an understanding of the regional trends of the Lower Yacimiento El Trébol Fm. Sandstones. These reservoir rocks yield the best oil shows in the offshore and they are among the most prospective and prolific onshore reservoir on the Golfo San Jorge Basin’s north flank. Detailed correlation enabled identification of three lower order sequences in this stratigraphic interval. These sequences are recognizable on seismic sections and well logs. The Lower Yacimiento El Trébol interval was regionally correlated from the offshore wells to the producing intervals at Escalante and El Trébol fields. No major truncations or stratigraphic wedges were identified on seismic lines or well logs, although the individual sequences that comprise this package can thin against some persistent structural highs. In addition, these sequences were correlated in 144 wells all around the north flank of the basin; sand thickness was measured from the SP curve in these wells. Net sand and sand percent maps were created. These maps demonstrate that lower Yacimiento El Trébol sandstones are concentrated in sand fairways in the Comodoro Rivadavia area and in the area south of the Marta wells. Conversely, there are many parts of the basin where Lower Yacimiento El Trébol Formation is represented by silts and shales (west and south of Comodoro Rivadavia and between Comodoro Rivadavia and Marta wells). Sand rich fairways, represented by gross thickness isopachs, map as trends that are perpendicular to the basin edges. Lower Yacimiento El Trébol production is found in these thick sand areas, while in thin sand areas, production comes from the underlying Comodoro Rivadavia Fm.