International reserves directly used for financing of balance of payments deficit and adjustment of the foreign exchange market disequilibrium. On the other hand, specific economic conditions of OPEC countries such as economic dependence on oil revenues, the lack of suitable flexibility in exchange rate regime and also oil shocks during recent decades, lead to effect of oil price volatility on international reserves in these countries. Hence, due to the important role of international reserves in economies and also the economic situation of OPEC countries, in this study by using mercantilist approach, the determinants of international reserves in OPEC countries have been evaluated with emphasizing on oil price uncertainty by using panel data method during 1980-2015. According to the results, moving average of real export revenue, the difference between domestic and international real interest rate, gross domestic product per capita, exchange rate regime index, trade openness, net barter terms of trade index, short-term external debt, capital account liberalization index, oil price uncertainty, positive and negative shocks of oil price have been known as determinants of international reserves.