Iran once was OPEC's second-leading producer, after Saudi Arabia, but output has plunged since 2012, when international sanctions forbade any country or energy company to buy, ship, finance and insure its crude because of Tehran's nuclear program. In 2011, Iran's output was 3.7 million barrels per day. With the sanctions, production dropped to 1.2 million barrels per day.

Iran and six world powers – Britain, China, France, Germany, Russia and the United States – reached an agreement in July on controlling that program and lifting the sanctions, probably by early 2016. Oil Minister Bijan Zanganeh has said repeatedly that his country can quickly boost production by more than 1 million barrels per day within a month after the sanctions are lifted.

This could further depress the price of oil, which has dropped precipitously since summer 2014. Already there is a glut of oil, and OPEC members lately have been producing at near-record levels. The group already is exceeding its output cap of 30 million barrels a day by at least 1.5 million barrels per day. Once Iran returns to the market, the price probably will fall further.

So be it, Zanganeh said in Tehran on Aug. 23. "We will be raising our oil production at any cost and we have no other alternative," he was quoted by his ministry's website, Shana. "If Iran's oil production hike is not done promptly, we will be losing our market share permanently."

But Zanganeh also said he was aware that his country's return to the world oil market could further weaken prices, and declared Tehran's support of a call for OPEC to hold an extraordinary meeting to discuss ways to stabilize oil's price. The cartel's next scheduled meeting will be Dec. 4.