Saudi Arabia opened the taps in May, increasing its oil output ahead of a critical meeting of crude-producing nations that will determine whether it's time to unwind a deal to limit production.
The Saudis reported the supply spike following reports that the Trump administration sought assurances that Riyadh would raise output to offset the impact of Washington's renewed sanctions on Iran, Saudi Arabia's chief regional rival and OPEC's third biggest producer.
OPEC's top producer said it hiked output by 161,000 barrels a day in May. That brought the Saudis' monthly production to just over 10 million barrels a day, pushing it toward the ceiling it agreed to in November 2017.
The oil cartel's overall output was relatively steady, rising by about 34,000 barrels per day to nearly 31.9 million bpd, according to independent sources cited in OPEC's monthly report. That total reflects a Saudi output figure slightly lower than the kingdom reported itself, and a monthly jump that was roughly half as large.
To be sure, the increase is not proof that Saudi Arabia is getting ahead of OPEC policy before the wider group meets on June 22 in Vienna. The Saudis have also pumped well below their quota throughout the production-cutting agreement, which has been in place since January 2017. They also warned fellow OPEC members that their output exceeded 10 million barrels a day in May, Reuters reported this week.
However, reports of a possible arrangement between Washington and Riyadh appear to be fueling a rift between OPEC members that want to keep the deal in place and those that want to consider raising output.
On Monday, Iraqi oil minister Jabbar al-Luaibi said unilateral decisions by some OPEC members risk violating the production-cutting agreement, which is scheduled to last through the end of the year and includes nonmembers like Russia.
Iraq, along with Iran and Venezuela, have voiced support for maintaining the supply caps, which have boosted oil prices. The three nations risk losing market share because they currently lack spare capacity and would not benefit from a decision to ease the quotas.
OPEC said Tuesday that recent developments have created "pronounced uncertainty about the second half of the year."
According to OPEC "the re-emergence of global trade barriers, continued growing debt levels and potentially rising volatility in asset markets amid ongoing monetary tightening, are some of the challenges that may negatively impact the 2H18 growth dynamic."
OPEC raised its forecast for oil supply growth from non-members by 130,000 for 2018. It now expects countries outside OPEC to pump 1.86 million barrels a day above 2017 level. That means the world will need 300,000 fewer barrels per day from OPEC this year, the group projects.
Meanwhile, OPEC left its outlook for global oil demand unchanged at 98.85 million barrels per day, up 1.65 million bpd from last year. The group warned there may be limited scope for demand to exceed expectations.
"While oil demand in the US, China and India shows some upside potential, downside risks might limit this potential going forward, including a slowdown in the pace of economic growth in some major economies, stronger impact of policy reform with regard to retail prices, and further substitution toward natural gas," it said.
In April, oil stockpiles in developed nations were 26 million barrels below their five-year average, the level OPEC targeted when it agreed to cut output. However, the group added a caveat, noting that inventories are still 240 million barrels above the start of 2014, the year oil prices crashed.