Oil extended losses below $40 a barrel amid speculation a record global glut will be prolonged as OPEC effectively abandoned its longtime strategy of limiting production to control prices.

Oil headed for its largest monthly drop Nov. 30 since July as Iran signaled the Organization of Petroleum Exporting Countries won’t reduce its production target at a meeting this week.

The average price of crude sold by OPEC fell below $40 a barrel for the first time since 2009, underscoring the financial cost of the group’s strategy to defend its market share.

OPEC trimmed estimates for supplies from outside the group in 2016 as the slump in prices takes its toll on the U.S. shale-oil industry.

The global oil glut will last through 2016 as the strongest demand growth in five years and faltering supply fail to clear the surplus, according to the International Energy Agency.

Crude closed at the lowest level in more than six years in New York as OPEC production climbed while China’s devaluation of the yuan bolstered concern that the world’s second-biggest economy will slow.

OPEC ministers extended their campaign to restrain rival oil producers by continuing to pump oil into a global supply glut and keeping their combined daily production target at 30 million barrels.