Iran was exporting about 2.5 million barrels a day at the end of 2011 and is now believed to be exporting about 1 million. Iradian said the price of oil averaged about $107 a barrel for the first half of the year but spiked in recent days over growing tensions in Syria, Iran's closest ally in the Arab world.
The steep drop in oil exports is not the only indication of the heavy toll sanctions have taken on Iran's economy over the past two years. The local rial currency lost two-thirds of its value since late 2011, and inflation has surged.
Since the election of new president Hasan Rouhani in June, there have been a number of indications the distress is deepening. Local news reports say Tehran may come up short of money to cover this year's budget. And an Iranian official said recently that more than $60 billion of the country's oil revenue is frozen in foreign banks and out of reach.
Still, analysts say Iran's economy has proved resilient and flexible enough to offset some sanctions damage. The country has diversified its exports and become less reliant on sanctioned oil.
Mark Dubowitz, director of the Foundation for Defense of Democracies and an advocate of tougher sanctions, said at the current trajectory Iran can continue to muddle through economically for a few more years. And some experts have concluded Iran could produce enough material to build a nuclear weapon by mid-2014.
"Without massively intensified economic pressure and a real threat of military force ... Iranian nuclear physics will continue to outpace Western economic pressure and diplomacy," Dubowitz said.