Excessive dependence of oil resource-rich countries on exporting a limited range of goods increases their economic vulnerability and threatens their economic stability and growth. Therefore, This study examines the effects of the exchange rate, natural resource rents, and comparative advantage on export diversification, within the export margin. For this purpose, dynamic panel data (DPD) from six OPEC member countries, including Iran, over the period 2016-2024 used and the Generalized Method of Moments (GMM) employed. First, the weighted average comparative advantage of nine export industries calculated and used as an index of comparative advantage creation for the studied countries to highlight its importance in restructuring exports. According to the results, the coefficient of comparative advantage indicates that allocating resources to industrial sectors and reducing dependence on raw material exports helps strengthen the export margin, and an increase in the exchange rate leads to growth in the export margin. On the other hand, natural resource rents have a negative effect, and increased dependence on primary goods exports threatens competitiveness. The findings indicate that exchange rate instability has a negligible impact on export diversification, exporters of industries with comparative advantage can significantly enhance the competitiveness of these countries.