State-owned Perusahaan Pertambangan Minyak Dan Gas Bumi Negara (Pertamina) controls the entire oil and gas industry in Indonesia, and is the world's largest producer and exporter of liquefied natural gas (LNG). Pertamina also works with foreign petroleum companies, but solely on a contract basis. The company has estimated proved reserves of 4 billion barrels of oil and 2.7 trillion cu. meters of natural gas, and operates seven oil refineries, and has numerous LNG, LPG, shipping, and fuel businesses. The company also invests heavily in the development of geothermal energy as an alternative energy source.