Since the onset of the EU embargo on Iranian crude, which took effect on July 1, oil shipments have plunged by 52%, or 1.2 million barrels a day.
The oil embargo bars the purchase, transport, financing and insuring of Iranian crude.
The measure is expected to cost the Islamic Republic some $48 billion in annualized revenue – some 10% of the country's economy.
The oil embargo "has been an unqualified success," Mike Wittner, head of oil-market research for the Americas at Societe Generale SA, said.
"There were a lot of concerns sanctions could backfire by causing an oil-price spike, but in the end the US and Europeans got their cake and they ate it too, because volumes are down and prices are down."
Iran currently exports 1.1 million oil barrels a day, down from an average of 2.3 million in 2011. The lost sales are valued at $133 million a day.
Daily oil output also noted a drop, falling 9.5% in July to 2.86 million barrels – Iran's lowest production level since February 1990.