Sanctions and underinvestment have reduced Iran's oil production capacity by at least 300,000 barrels per day, depriving the country of billions of dollars of revenues.
The slow development of new oilfields and the poor condition of many existing wells have caused the fall, according to Iranian and western experts.
“Oil production capacity has dropped by probably about 300,000-400,000 bpd,” said a former senior official in Iran's government. His figures were consistent with those of a western oil official. The period over which the decline has taken place is uncertain. Oil industry experts, however, say it has come about since Mahmoud Ahmadi-Nejad became president in 2005.