Iran came to Vienna seeking lowered output to raise prices, while the Saudis were looking to increase production to make crude more affordable. On paper the decision to keep output targets steady was meant to find a compromise between the two positions. But OPEC members normally ignore the official quota — the organization's daily output is now estimated at nearly 32 million barrels.

OPEC Secretary-General Abdullah Al-Badry told reporters that there was a "collective decision" to honor the 30 million barrel ceiling. But the Saudis, and others with capacity, were expected to keep overproducing to make up for any shortfall caused by the sanctions on Iranian oil.

Iran, in contrast, is faced with the prospect of having to cut its output of oil, which makes up nearly 80 percent of its foreign exchange earnings. Sanctions levied by the U.S. over Tehran's refusal to curb its nuclear program have already cut significantly into exports — from about 2.5 million barrels a day last year to between 1.2 and 1.8 million barrels now, according to estimates by U.S.