Phase seven is due to go on line by year end and phase eight in May.
The three phases will produce 104 million cubic metres (3.6 billion cubic feet) of sour gas, 158,000 barrels of condensates and 4,450 tonnes of liquefied petroleum gas per day.
"The revenue from the exports of condensates will be six billion dollars a year," the managing director of state-owned project developer Petropars, Gholam Reza Manouchehri, was quoted as saying.
The total value of all the products from the three phases amounts to 12 billion dollars annually, said Manouchehri.
The project is a joint one between Iranian and foreign companies, including Norway's Statoil.
The South Pars field in the Gulf has reserves of around 500 trillion cubic feet (14 trillion cubic metres), or some eight percent of the world total.
It has been divided into 28 phases, one through five of which have already gone on stream.
Iran expects to launch phases nine and 10 by the end of its current calendar year on March 20, 2009.
Most of the gas is slated for injection into oil fields of the southern province of Khuzestan to compensate for low pressure, which cuts the oil recovery rate.
However, the oil ministry has vowed that the new gas production projects this year will help covering domestic requirement in winter, when the country has previously faced supply cuts due to high consumption.
Iran's gas production capacity is expected to reach 532 million cubic meters (18.8 billion cubuic feet) a day in winter, but officials have warned of a consumption rate of more than 700 million cubic meters (24.7 billion cubic feet) in the period.
