The Eastern Llanos Basin (ELB) represents the richest oil-producing region in Colombia. With most of its potential for structural traps already exploited, stratigraphical and combined traps are becoming the main exploration target in the Basin, both for the Cretaceous and Cenozoic sequences. In the SouthCentral ELB, the Late Paleocene Unconformity is represented by a complex network of incised valleys that were eventually filled-up by a thick (up to 400ft) section of Oligocene tide-dominated paralic transgressive deposits. Despite the excellent production and reservoir properties, this Oligocene reservoir revealed complex compartmentalization and an intricate distribution of fluid contacts and pressure regimes. This cannot be explained by structural traps or simple stratigraphic correlations. Based on seismic interpretation, sequence stratigraphy and facies analysis of cores, cuttings and well logs, it was possible to delineate a predictable model for internal sedimentary architecture. Two main depositional cycles separated by a regional flooding event were identified. The older cycle represents the initial infill of an incised valley network with fluvial-tidal influence. The younger cycle consists of estuarine-deltaic deposits with strong tidal control. Each cycle exhibits very distinct depositional geometries and correlation surfaces when observed in the seismic data. At well log scale, an internal architecture involving natural fluid boundaries was interpreted, responsible for the multiple fluid contacts and pressure regimes. This case-study can be applied to similar exploration and production scenarios and regarded as a methodology to evaluate the internal complexity of such stratigraphic/ combined traps