Oil wells are mainly found in the western lowlands. This area also produces associated natural gas. The main oilfields are Cheleken, Gonurdepe, Nebitdag, Gumdag, Barsagelmez, Guyujyk, Gyzylgum, Ordekli, Gogerendag, Gamyshlyja, Ekerem, Chekishler, Keymir, Ekizek, and Bugdayly. Oil is also produced from offshore wells in the Caspian Sea. Most oil is extracted by the Turkmenistan State Company (Concern) Türkmennebit from fields at Goturdepe, Balkanabat, and on the Cheleken Peninsula near the Caspian Sea, which have a combined estimated reserve of 700 million tons. Much of the oil produced in Turkmenistan is refined in the Turkmenbashy and Seydi refineries. Some oil is exported by tanker vessel across the Caspian Sea en route to Europe via Baku and Makhachkala. Foreign firms involved in offshore oil extraction include Eni S.p.A. of Italy, Dragon Oil of the United Arab Emirates, and Petronas of Malaysia.