The Villeta-Caballos(!) and Villeta-Monserrate(!) petroleum systems of the Neiva area, situated in the upper Magdalena Valley of central Colombia, cover 5120 km² and include 18 fields with ultimate recoverable reserves of 83.8 million m³ (527 million bbl) of oil and 5.7 billion m³ (201 bcf) of gas. Aptian-Holocene sedimentary rocks in the area were deposited in rift, margin sag, and foreland basins. Geochemistry data show that the hydrocarbons were generated mainly from two intervals within the Albian-Santonian Villeta Formation. Thermal maturation modeling indicates that the hydrocarbons were generated from a pod of active source rock along the footwall of the Chusma fault (Villeta-Caballos system) and in the central Neiva syncline (Ville a-Monserrate system) from the end of the Oligocene to the present. Overburden rocks are mostly Eocene-Pleistocene molassic sedimentary rocks. The two main reservoirs are Cretaceous sandstones of the Caballos and Monserrate formations. Secondary reservoirs of significance are fluvial sandstones of the Miocene Honda Group. Traps are mainly structures (anticlines and faulted anticlines) associated with a fold and thrust belt that began in the Oligocene and is still active.

Essential elements and processes of these petroleum systems in the Neiva area occurred from the Aptian (110 Ma) to the present. First, the fluvial sandstones of lower Caballos reservoir rock were deposited. The source rock was deposited a few million years later and reached thermal maturity in synchronism with the formation of structural traps during the last 25 m.y. Destruction of some accumulations in the Villeta-Caballos system by uplift and erosion of reservoir rocks in the Monserate Formation in the fold belt started in the Miocene. The volume of hydrocarbons generated by both systems was calculated using an average TOC content of 2.1 wt. % for 235 m of total source interval in two intervals and a total area of mature source of 1650 km². A hydrocarbon generation of 325 mg HC/g TOC was used based on the HI measurements of immature Villeta source rock and a hydrocarbon generation algorithm. The generation-accumulation efficiency of the systems is about 5%.