There are three onshore sedimentary basins in Guatemala and the most important as far as petroleum is concerned is the Peten Basin. This basin covers an area of over 23,000 square miles and is under explored. A relatively late structural high known as the La Libertad Arch divides the basin into northern and southern sub-basins.
In the South Peten Basin more than 30,000 feet of sediment has accumulated since Permian times. Little is known about the Permian and Jurassic sediments because so few wells have penetrated them and the main oil reservoirs lie within the Cretaceous sediments. In the Peten Basin these Cretaceous rocks are called the Coban Formation which is further divided into Coban A, B, C and D members. They consist of interbedded limestone, dolomites and anhydrites and most of the oil reservoirs discovered to date have been in fractured dolomites in the Coban B, C and D members. Significant production also occurs from these reservoirs in the Chiapas area of southern Mexico.
The source rocks for oil have not been definitively identified but they are thought to include carbonates of the Coban A. Good quality Jurassic age marine sediments may also generate oil in the Peten Basin.
Seal is provided by the anhydrites within the Coban Formation and the interbedding of reservoir and seal allows for the formation of stacked oil accumulations.