Separately, Oil Minister Massoud Mirkazemi said the Islamic Republic's state oil industry has about $80 billion worth of incomplete projects following last year's crude price fall and he called for increased private sector involvement.
Their comments underlined Iran's need of capital to help develop its all-important energy sector, in the face of U.N. and U.S. sanctions which are deterring many Western investors, even though oil prices have recovered this year.
"With the drastic drop in the price of crude oil (in 2008) the execution of many oil projects ceased," the semi-official Mehr News Agency quoted Mirkazemi as saying.
Ali Vakili, managing director of Pars Oil and Gas Company, said more than $30 billion had been invested in various South Pars projects since the 2007-2008 Iranian year, Mehr reported.
"And we estimate about $40 billion for remaining phases … we predict that we would be able to develop all phases within a 10-year period," Vakili said. The Iranian year starts in March.
The South Pars field is part of the huge formation shared with Qatar that makes up the world's largest pure gas reserve. The Iranian part is divided into 24 phases.
But Iran, which is also the world's fifth-largest crude exporter, has struggled to find the cash and the technology to develop this and other fields as international sanctions and political pressure have kept foreign firms away.
Iran has almost 16 percent of the world's total gas reserves, but currently has no major net exports.
It is drawing interest from Indian, Chinese and other Asian firms seen as less susceptible to international pressures but industry experts say it will be many years before Iran becomes a major gas exporter.
Citing Oil Ministry officials, Mehr said the energy industry will need $200 billion in investments in new oil, gas and petrechemical projects by the end of the fifth five-year development plan in 2015.
"In the oil industry's needed investment for downstream sectors, the private sector must take action and make investments," Mirkazemi said, reiterating Iran's plans to issue bonds worth 1 billion euros. (Reporting by Reza Derakhshi and Hashem Kalantari; writing by Fredrik Dahl; editing by David Cowell)
