The current Iranian year started on March 21, 2009.
"Iran's oil and gas revenue has reached $31.3 billion (in the six months from last) March — some $26.2 billion lower than the same period in the last Iranian year," Bahar said, citing a Central Bank report.
Iran is the world's fifth-largest crude exporter and its economy mainly relies on the country's oil and gas exports.
The Central Bank also reported a decrease in the value of non-oil exports, which amounted to about $9.1 billion from March to September 2009, some $0.7 billion lower than in the same period in 2008.
President Mahmoud Ahmadinejad's adviser in charge of the country's budget, Rahim Mombini, said Iran's national budget income for the next Iranian year had been projected at around $59.6 billion. In Iran's budget for next year, oil exports are estimated to generate about $39.6 billion.
Critics accuse Ahmadinejad of squandering the windfall oil revenue Iran earned when crude prices soared in 2008, making the Islamic state weaker in the face of sanctions imposed on it over its disputed nuclear activities.
In January, Ahmadinejad submitted a $368 billion budget bill to parliament for the next Iranian year.
He said the 2010/11 national budget would be less reliant on oil income.
The United States and its European allies are planning to impose further sanctions on Iran after it failed to meet the U.S. Dec. 31 deadline to accept a U.N.-brokered proposal to send its uranium abroad for processing.
The West fears Iran is seeking nuclear bombs under cover of a civilian programme. Tehran denies this, saying it needs nuclear technology to generate electricity to meet the country's booming demand.
The parliament approved the government's subsidy reform plan in December, which if implemented, will mean food and energy subsidies ending in five years time. Critics believe the plan will harm Iran's already weak economy by fuelling inflation, which stands around 14 percent. (Writing by Reza Derakhshi; editing by Stephen Nisbet)
