In the Lower Indus Basin's Cretaceous petroleum system, the Upper Goru Shale (Cretaceous, Upper Cretaceous) serves as the primary seal (cap) rock. The reservoir is the Lower Goru sandstone (fluvio-deltaic sandstones). This system is the most prolific in Pakistan, accounting for the majority of gas production. The Sui gas field (largest in Pakistan) produces from Eocene Sui Main Limestone, but Cretaceous fields use the Goru shale seal.