June Brent crude on London's ICE Futures exchange fell $0.49, or 0.9%, to $55.40 a barrel. On Thursday, before major markets closed for the holiday break, they settled up 3 United States cents at US$55.89 a barrel.
U.S. West Texas Intermediate crude futures were also down 18 cents at $53.
Crude oil prices were pulling close to even in early trading Monday, following weakness overnight sparked by lingering US energy sector gains.
While compliance has been strong among OPEC countries, production cuts have lagged among other producers including Russian Federation.
Gas prices seemed to find level ground over the weekend after increasing for more than two weeks, the auto club AAA said this week. "The drop in tensions following North Korea's failed missile test. have seen oil fade in Asia", said Jeffrey Halley, senior market analyst at futures brokerage OANDA in Singapore.
As a result, March's global oil supply fell, according to the International Energy Agency.
$60 barrel prices would allow for additional investment in the worldwide energy sector, without allowing the United States' shale producers too much additional financial leverage to undo the effects of the output cuts.
Although the failure of a ballistic missile launch in North Korea brought some respite, markets were braced for further tensions in the region. The official inventory report, courtesy of the U.S. Energy Information Administration (EIA), will be released the following morning.
Non-OPEC oil producers such as Azerbaijan, Bahrain, Brunei, Equatorial Guinea, Kazakhstan, Malaysia, Mexico, Oman, Russia, Sudan, and South Sudan agreed to reduce output by 558,000 bpd starting from January 1, 2017 for six months, extendable for another six months, taking into account prevailing market conditions and prospects.
China on Monday reported first quarter GDP rose 1.3% on the quarter compared to the same period a year ago for an annual pace of 6.9%, beating expectations for the year comparison. Forecast-beating March investment, retail sales and exports all suggested China's economy, the world's second-largest oil consumer, may carry solid momentum into spring.
Analysts say buying was suppressed by data showing that the USA oil rig count rose for the 13th straight week (http://www.marketwatch.com/story/baker-hughes-data-show-us-oil-rig-count-up-a-13th-week-in-a-row-2017-04-13) in the week of April 13.
China's March refinery throughput also rose to 11.19 million bpd, just shy of December's record, as margins remained attractive.