Qatargas is the world's largest liquefied natural gas (LNG) company. It produces and supplies the globe with 42 million metric tonnes of LNG annually from across its four ventures—Qatargas 1, Qatargas 2, Qatargas 3, and Qatargas 4. It is headquartered in Doha, Qatar, and maintains its upstream assets in Ras Laffan, Qatar.

Natural gas is supplied to Qatargas's LNG trains from Qatar's North Field, by far the world's largest non-associated gas field. 

Qatargas (Qatargas Liquefied Gas Company Limited) was established in 1984 as a joint venture between Qatar Petroleum, ExxonMobil and other partners. In the following years the company began developing the North Field and erected the first three LNG trains (Train 1, 2 and 3) with a design capacity of 3.3 million tonnes per year each.

The trains were built in 1996, 1997 and 1998 respectively.

The shareholders of the Qatargas 1 are Qatar Petroleum, ExxonMobil, Total, Mitsui and Marubeni.  

Qatargas II, a joint venture of Qatar Petroleum and ExxonMobil, owns LNG trains 4 and 5 with a capacity of 7.8 million tonnes per year each. It is supplying LNG for the South Hook LNG terminal at Milford Haven, Pembrokeshire, Wales, from where gas is fed to the South Wales Gas Pipeline. This covers 20% of the United Kingdom's needs of LNG.

Qatargas III is a joint venture between Qatar Petroleum, ConocoPhillips and Mitsui. Qatargas IV is a joint venture between Qatar Petroleum and Royal Dutch Shell.

At first approached as separate projects, Qatargas III and IV are now being built by a joint asset development team that is staffed by Qatargas, ConocoPhillips and Shell employees as well as project direct hires and short term contractors. Its trains have started up by end 2010 (QG3) and early 2011 (QG4). 

Accoring to en.wikipedia