The countries collectively decided at the end of 2016 to limit their oil output by 1.8 million barrels a day. The agreement was extended for the second time on November 30 to end-2018. The agreement will be reviewed again next summer.
OPEC has often had trouble enforcing agreed production ceilings on its members, but compliance with the current arrangement seems to have been quite good. Rising oil prices, up about 25 % y-o-y in January-November, have been to a degree supported by the deal. The Brent oil price in early December has been around 63 dollars a barrel.