The pledge from Saudi Arabia and Iraq, the first and second largest OPEC producers, came after their oil ministers met in the Red Sea city of Jeddah.
Saudi Energy Minister Khalid al-Falih and his Iraqi counterpart Jabbar al-Luaybi also vowed to ensure coordination of their nations' oil policies, according to the Saudi Press Agency, as the Arab neighbours seek to upgrade strategic ties.
OPEC states and other oil producers agreed in November to cut output until March 2018, in its long-haul gambit to erode a world oil glut and boost prices.
Output from the 14 cartel members hit 32.87 million barrels per day (mbd) last month, OPEC said in its monthly report on the oil market, up from 32.69 mbd in June.
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The inability of some members to cut ouput has raised doubts about OPEC's capacity to enforce the November deal.
Saudi Arabia and Iraq have suffered huge economic pain because of sliding oil prices.
Luaybi's visit symbolises a growing rapprochement between Riyadh and Baghdad as the kingdom seeks to increase its influence in Iraqi politics and undercut the say of regional rival Iran.