The North Celtic Sea Basin lies off the southeast coast of Ireland, extending through Saint George's Channel to Cardigan Bay. The basin is gas-prone, and the main reservoirs are Late Jurassic and Early Cretaceous sandstones. The Early Cretaceous Wealden Formation has proved to be the most attractive exploration target, including the large Kinsale Head gas field discovered in 1971. Although large areas remain unexplored, the basin is considered relatively mature and the with the main prospective areas are thought to be in the centre of the basin. Future exploration is expected to be on a relatively small scale, and carried out by companies already in the basin. In recent years, the introduction of more attractive fiscal terms has attracted smaller companies. Their primary focus has been on commercialising existing heavy oil discoveries, and participating in the Kinsale Head, Ballycotton and Seven Heads Gas fields.