This paper proposes two petroleum systems in the Baja Guajira Sub-basin: 1) The Upper Cretaceous FormationCastilletes Formation system and 2) The Siamana FormationMacarao Formation-Castilletes Formation system. Geochemical models in two dimensions, calibrated with thermal maturity data, indicate that hydrocarbons have been originated at the base of the stratigraphic sequence and have migrated upward. The critical factor in determining the formation of the Chuchupa and Ballena gas field was the presence of sealing beds in the top of the Castilletes Formation. Well information from the Baja Guajira Sub-Basin reveals a relatively absence of low permeable strata explaining the scatter occurrence of gas field in the Guajira Sub-Basin. The geochemical information along with the geochemical models allow to locate the best prospective area for hydrocarbons, which is located toward the norwest of the Baja Guajira Sub-basin in the offshore region, where it is expected the presence of several hydrocarbon kitchens.