Opec has cut less than half the 1.2 million barrels per day of oil agreed last month and with prices still near $60 some countries may be pumping more crude at the expense of more disciplined members.
"Prices have fallen but at current levels they are still earning very, very good money," said Leo Drollas of the Centre for Global Energy Studies. "I'd expect Opec to cut by about 400,000 bpd into December."
Saudi Arabia, the world's largest oil exporter, is shouldering the bulk of the reduction. Its customers say they have already been informed of cuts amounting to 380,000 bpd. Gulf neighbour the United Arab Emirates, whose share of the reduction is 101,000 bpd, has also notified customers of a cut in supplies. Kuwait is also expected to curb output.
But Nigeria, the Opec member that first called for cuts and the group's current president, plans to increase its exports from December 1 rather than lower them, traders say. Analysts suspect other members may be quietly ignoring the deal. Indonesia has broken ranks publicly.
Opec's first plan to trim output since 2004 comes after a price slide from a July record of $78.40 alarmed oil ministers. It has no formal mechanism to ensure members stick to agreements. "The history is that they get about 60 percent of what they agree to on paper," said Adam Sieminski, chief energy economist Deutsche Bank in New York.
"Our traders say that most of their counterparts believe there won't be any cuts at all, while analysts seem to think that some 600,000 bpd is likely to come off and that maybe half of that is already off." The Organisation of the Petroleum Exporting Countries, source of more than a third of the world's oil, agreed to cut supply with effect November 1 at a meeting on October 19-20 in Qatar. Despite public announcements from oil ministers and state oil companies of other Opec members, their actual reduction in supply is much more difficult to measure.
Nigeria pre-empted Opec's agreement when it told customers to load 5 percent less oil in October. But buyers said they were then offered top-ups at premium prices.
The world's eighth-largest oil exporter is scheduled to ship 2.09 million bpd of crude in December, up 50,000 bpd from the previous month, traders said on Tuesday.
Buyers of Libyan and Algerian crude also said they had yet to receive notice of any cuts. Opec's second-smallest producer, Indonesia, has said it will not cut supply. The time between oil production in the Middle East and its arrival by ship in top consumer the United States means it will be weeks before investors can gauge the size of the reduction.
Opec itself says it is too soon to discuss compliance with the cutback. Some members have said the group may need to trim supply further at its next meeting on December 14 in Nigeria. "We have to wait for at least a month to review production and see who is doing what," Acting Secretary-General and Nigerian official Mohammed Barkindo said on Tuesday in Moscow.