OPEC has criticized unidentified non-member countries for their refusal to cooperate with the oil exporter group in propping up prices and repeated its call for them to do so. “In the past, OPEC has often shouldered the burden of ensuring oil market stability alone. The Organization of the Petroleum Exporting Countries last year refused to cut its oil output after non-member countries including Russia declined to offer output curbs, deepening a slide in oil prices.