Crude oil prices declined heavily in early trading Monday after OPEC data show the dynamics of global supply and demand remain unchanged.

For nearly two years, crude oil markets have been pressured by global economic growth that was too slow to take up the heavy supply of energy products. By May, the International Energy Agency said some level of balance was returning to the market as supplies where fading against slow increase in overall demand.

Crude oil prices are up 7 percent from May and 90 percent higher than their low point for the year as the glut of oil that persisted on the market for the last two years starts to fade.

In its monthly market report for June, the Organization of Petroleum Exporting Countries reported demand growth for 2016 was expected at 1.2 million barrels per day, a level unchanged from the May report. For supplies, the global average forecast of the year was unchanged at 56.4 million bpd.

Supply disruptions in Canada, Nigeria and elsewhere were "broadly offset" by gains in countries outside the 13-member production group, OPEC said.

Crude oil prices dropped heavily on word of the market standstill, continuing from the heavy losses reported during the latter half of last week. The price for Brent crude oil was down from the previous close by 1.5 percent to start the day at $49.75 per barrel. West Texas Intermediate, the U.S. benchmark for the price of oil, lost 1.4 percent to open in New York at $48.35 per barrel.

WTI traded above $50 only for contracts from November and beyond.

Global markets as a whole are moving lower as investors look for safe haven before the June 23 referendum on whether the United Kingdom remains in the European Union. Last week, Angel Gurria, the secretary-general of the Organization for Economic Cooperation and Development, that if the so-called Brexit strategy emerges successful from London, long-term growth for the European Union could be jeopardized.

From OPEC's perspective, the prospects for the European economy are "muted" as the vote on the exit from the European Union presents uncertainty about momentum during the second half of the year.