U.S.-led sanctions against Iran are costing OPEC’s third-largest producer $133 million a day in lost sales without raising global crude prices, handing President Barack Obama an election-year foreign-policy victory.

Shipments from Iran have plunged by 1.2 million barrels per day, or 52 percent, since the sanctions banning the purchase, transport, financing and insuring of Iranian crude began on July 1, according to data compiled by Bloomberg News. Annualized, that would cost President Mahmoud Ahmadinejad’s country about $48 billion in revenue, equivalent to 10 percent of its economy.

While Iran’s threats to disrupt the flow of oil through the Persian Gulf sent crude to a three-year high in March, increased production from Saudi Arabia, a U.S. output boom and the slowing global economy have left prices 1 percent lower in 2012. That’s helping Obama avoid steeper domestic fuel costs before the November presidential election. Iran has to contend with a weakening currency and rising unemployment.

“It’s been an unqualified success,” Mike Wittner, head of oil-market research for the Americas at Societe Generale SA, said in a telephone interview from New York on July 25.

“There were a lot of concerns sanctions could backfire by causing an oil-price spike, but in the end the U.S. and Europeans got their cake and they ate it too, because volumes are down and prices are down.”

Voter concern about fuel costs has plunged since Republican Mitt Romney, Obama’s presumptive challenger, called for firing top officials he blamed for rising gasoline prices in a March 18 interview on “Fox News Sunday.”

In a monthly Gallup poll on the most important issues facing the U.S., 1 percent of respondents cited fuel or oil prices in questioning on July 9-12, compared with 8 percent in an April 9-12 survey.

Regular unleaded gasoline at the pump, averaged across America, fell 10 percent to $3.534 a gallon on Aug. 1 from the 2012 high of $3.936 reached on April 4, according to data from Heathrow, Florida-based AAA, the largest U.S. motoring group.

Brent oil has dropped 3.8 percent to $106.34 a barrel since Jan. 23, when European Union ministers approved a ban on the purchase and insurance of Iranian oil. The U.S. is paying 6.2 percent less than a year ago for imported crude as domestic fields produce the most in 13 years, driving stockpiles to all-time highs, Energy Department data show.

Crude futures in London rose as high as $128.40 on March 1, an advance of 20 percent for the year, after Iranian officials threatened to order the closing of the Strait of Hormuz. The Gulf waterway, 34 kilometers wide at its narrowest, is a conduit for 20 percent of the world’s traded oil, according to the Washington-based Energy Information Administration.

Prices retreated as Saudi Arabia boosted output. The Organization of Petroleum Exporting Countries’ biggest producer is pumping more than 10 million barrels a day, the most in three decades and 22 percent more than at the end of 2010, according to the International Energy Agency. The Paris-based adviser to the world’s biggest industrialized economies cut its forecast for global oil use four times this year, to 89.9 million barrels a day.

Iran is exporting 1.1 million barrels a day of oil, according to the median estimate of 10 analysts compiled by Bloomberg, down from an average of 2.3 million in 2011. The lost sales are valued at $133 million a day, based on the 2012 average price of $110.60 a barrel for Iran Heavy crude in Asia, according to Bloomberg data.

Daily output fell 9.5 percent in July to 2.86 million barrels, the lowest level since February 1990, a Bloomberg survey showed last month. Iran dropped to third among OPEC’s biggest producers, after holding the No. 2 spot since May 2000.

Prices of meat, rice and bread have spiraled in Iran as the riyal lost a third of its value against the dollar on the open market since November. Inflation accelerated to 22.4 percent in the 12 months through June 20, according to the central bank.

Unemployment reached 13.5 percent in March, the Shargh newspaper reported, citing figures from the national statistics bureau. The jobless rate was 11.9 percent in 2010, according to the International Monetary Fund.

Economic growth will slow this year to 0.4 percent, from 2 percent in 2011, the IMF said July 16. Gross domestic product is expected to accelerate to 1.3 percent in 2013, with unemployment set to rise over the next two years, according to IMF forecasts.

The international sanctions are “the harshest ever imposed on a country,” Ahmadinejad said on July 3. Oil accounts for half of Iran’s government revenue, according to the EIA.

U.S. and EU sanctions have a global reach, thwarting financial transactions with Iran’s state entities and blocking insurance for oil shipments to Asia, the biggest market for Iranian crude. A U.S. law that took effect June 28 threatens to cut access to dollars for any foreign bank settling oil trades with Iran. China, Japan, India and 17 other countries received renewable 180-day waivers for reducing imports.

The U.S. president announced an executive order on July 31 extending sanctions to buying Iranian petrochemical products, providing material support to the National Iranian Oil Co. or Central Bank of Iran, and acquiring U.S. bank notes or precious metals by Iran’s government.

The Treasury Department also said the Bank of Kunlun in China and Iraq’s Elaf Islamic Bank helped Iranian firms conduct transactions worth millions of dollars and blocked the offenders from the U.S. financial system.

Congress is set to give final approval to legislation aimed at preventing Iran from repatriating oil revenue, with measures against everything from conducting oil-for-gold swaps with the country to helping it mine uranium.

The U.S. has limited dealings with Iran since 1979, when militants took 52 hostages at the American Embassy in Tehran. The United Nations levied four sets of sanctions against Iran starting in 2006. None had the teeth to curb sales, and in 2007 the country’s crude exports rose to an 11-year high of 2.6 million barrels a day, according to Energy Department estimates.

Restrictions on supplying equipment and technology have stymied plans to modernize refineries and develop the world’s second-largest natural-gas reserves.

Iran lacks the expertise to build the liquefaction plants needed to boost gas exports and prolonged sanctions may hurt its ability to maintain and expand oil production, according to Robin Mills, head of consulting at Dubai-based Manaar Energy Consulting and Project Management and a former Iran specialist at Royal Dutch Shell Plc.

The EU ban prevents most tankers from sailing to the country because the global marine-insurance industry is concentrated in London. All but 5 percent of the world’s fleet is insured by members of the London-based International Group of P&I Clubs, and the Islamic Republic doesn’t have enough ships of its own to compensate, according to Dahlman Rose & Co., a New York investment bank.

China, Iran’s biggest customer and an opponent of sanctions, imported more crude from the Persian Gulf producer in June than its monthly average for 2011. Since the July embargo, Iranian tankers able to carry at least 20 million barrels have signaled for the Asian nation, ship-tracking data compiled by Bloomberg show. The world’s second-largest oil consumer hasn’t sent any of its own ships since July 1, and the government in Beijing hasn’t said if it will insure cargoes.

“The future of Iran’s oil exports hinges on whether China is going to use its own ships,” said Nigel Prentis, the London- based head of research at HSBC Shipping Ltd.