Platts survey of Opec and oil industry officials and analysts showed that May production marks a rise from April's output level of 31.71 million b/d and is the highest level since October 2008 when Opec volumes averaged 32.26 million b/d.
"The number that really matters is the jump from January to May this year, which shows that Opec output rose from 30.87 million b/d in January to 31.75 million b/d last month," said John Kingston, Platts global director of news.
"This has occurred even as Iranian supplies were being squeezed by a drop in the number of customers willing to take its oil. We can now assume Opec members at least will discuss at their upcoming meeting a possible paring of production. This scenario was almost impossible to fathom just a few months ago, as Opec continues to surprise the world with its ability to put oil on to the market," Kingston said.
The survey showed that Iranian output was 3.25 million b/d in May, down from 3.28 million b/d in April. Iran's crude exports to Europe already have fallen ahead of a European Union ban on Iranian crude imports set to come into full effect on July 1.
Saudi Arabia is Opec's largest exporter. Saudi Arabia boosted output 50,000 b/d to 10 million b/d in May, according to the survey.