OPEC+ has delayed a review of members’ oil production capacity after the Iran war disrupted projects to expand output across the Middle East, creating uncertainty over estimates that will help set 2027 quotas, according to two sources familiar with the matter.

The group had ordered the review in late 2025 ahead of setting 2027 production quotas, with completion originally due by the end of September 2026. The deadline has now slipped, with one source expecting the assessment to finish by mid-November. OPEC+ did not immediately respond to a request for comment.

OPEC said in June it affirmed “the importance of completing the maximum sustainable production capacity (MSC) assessment for all (member) countries to be used as reference for 2027 production baselines.”

US petroleum consultant DeGolyer and MacNaughton is conducting the capacity assessment for OPEC+ members except Russia, Iran, and Venezuela, which are under US sanctions, according to sources. One source said the company will submit its report by mid-November, allowing OPEC+ to consider the findings at its next group-wide meeting in late November.

The review has become more difficult as the conflict delays projects that were expected to increase production capacity in some member states. The sources said some countries have also yet to submit required data. The assessment could influence future quotas, with producers facing lower capacity potentially seeking lower allocations, while those adding capacity could seek higher quotas.

Earlier in September, OPEC+ kept its October oil output policy unchanged as the Iran war continued to restrict crude flows through the Strait of Hormuz. The group is due to meet again on October 4, while another layer of production cuts remains in place through the end of 2026.