Gholamreza Kateb, a spokesman for the parliamentary planning and budget committee, was quoted by the state-run Iranian Students' News Agency as saying revenue from oil and natural gas condensates dropped 45 percent since to start of the Iranian year in March.
A "considerable decrease" is expected to continue, reports Bloomberg News.
Iran's consumer base has contracted substantially because of sanctions imposed by Western governments concerned about Tehran's nuclear ambitions. The U.S. government has issued sanctions waivers to country's that show a considerable decline in Iranian crude oil purchases.
Last month, the International Energy Agency said it expected Iranian oil exports to dip to 1 million barrels per day for January because of a decline in foreign sales. The country pumped 2.6 million bpd in December, a decline of 40,000 bpd from November.
Records reviewed by Bloomberg suggest Iran is the No. 5 oil producer among members of the Organization of Petroleum Exporting Countries. It once held the No. 2 position behind Saudi Arabia.