OPEC’s struggle with the first step of its new production deal — agreeing on how much its members are pumping — deepened as Iran became the third nation to openly question the organization’s data. Output estimates compiled by OPEC’s Vienna-based secretariat are “not acceptable,” Ali Kardor, managing director of National Iranian Oil Co., said Monday in Tehran. Iran is pumping 3.89 million barrels a day, Kardor said, or about 300,000 a day more than OPEC estimated the country produced last month. Iraq and Venezuela have already criticized the data, which OPEC compiles from “secondary sources” such as news agencies. The Organization of Petroleum Exporting Countries aims to finalize an accord to cut production, the group’s first reduction in eight years, when members convene in Vienna at the end of next month. Yet as nations squabble over how much they’re producing, it will be increasingly difficult to agree on how […]