Iran plans to invest around $70 billion in two major offshore natural gas fields in the 2010-15 period, a senior official said in comments broadcast on Friday.
Seifollah Jashnsaz, managing director of the state National Iranian Oil Co (NIOC), said Iran would invest $40 billion to complete remaining projects in the South Pars field during the fifth five-year economic plan, which runs until 2015.
He did not say how Iran, which is also the world's fifth-largest oil exporter, would finance the investments.
For years it has struggled to develop its reserves and now has to contend with an international lack of credit, as well as problems specific to Iran, which is under international sanctions due to its disputed nuclear programme.
Iran has increasingly turned to Asia, which in some cases still has available cash to invest and whose energy demand is expected to outpace that in the developed world.
Another Iranian official, Hojjatollah Ghanimifard, told news agency Reuters on Monday Iran is in talks with Asian banks on a 1 billion euro ($1.40 billion) bond to finance the development of South Pars, as part of its pursuit of billions of energy sector funding.
The Iranian government has agreed to the Oil Ministry's proposal to issue such a bond to fund South Pars' development, the semi-official Mehr News Agency reported on Friday.
South Pars, the world's largest reservoir of gas, is shared by Iran and Qatar. The Iranian part is divided into 24 phases.
An additional $25 billion would be invested in the North Pars field, Jashnsaz said.
"Altogether it looks like ... Iran will invest some $70 billion in these two fields which is a very high figure and no other field in the country is expected to have such high investment," Jashnsaz told state television.
He did not explain the difference between the $70 billion figure and the total of $65 billion which he said would be invested in the two fields.
In May, an Iranian state firm said Iran planned to issue $12.3 billion of foreign currency and rial-denominated bonds over the next three years to help finance South Pars.
In all, Iran's five-year energy sector investment plan required investment totalling around $30 billion per year, Ghanimifard had told Reuters in an interview.
Iran has the world's second largest gas reserves, almost 16 percent of the world's total, but currently has no major net exports partly because U.S. and U.N. sanctions have deterred investment by Western firms with expertise and technology.