EIA, the statistical arm of the Energy Department, updated its country profile for Iran. The report, published one day after the U.S. Treasury Department said sanctions relief for Iran will continue through November, said investors may face restrictions in Iran's energy sector.
"International sanctions continue to affect foreign investment in Iran's energy sector, limiting the technology and expertise needed to expand the capacity at oil and natural gas fields and reverse production declines," the report said.
Iran under the terms of an agreement reached with Western powers in November 2013 secured relief from some sanctions on its energy sector in exchange for a pledge to curb its nuclear research activity.
Iran can export around 1 million barrels of oil per day according to the terms of the deal.
EIA estimates Iranian oil production has increased by nearly 200,000 barrels per day during the first half of the year compared with the annual average for 2013. The administration's Tuesday report said preliminary export data show a similar increase in exports for 2014.
EIA says Iran holds an estimated 157 billion barrels of crude oil reserves, or about 10 percent of the world's total. More than 75 percent of the oil reserves were discovered before 1985.