This research looks into the accumulation of foreign exchange reserves and the development of the macro-economy in the Gulf and Cooperation Council countries (GCC countries), namely, Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates. Using yearly data covering the period from 1996 through 2015, the empirical results show positive and significant relationships between foreign exchange reserves accumulation on one hand, and oil prices, GDP, the ratio of current account to GDP, and the ratio of broad money to GDP on the other hand. Moreover, the results point to negative and significant relationships between foreign exchange reserves accumulation on one hand, and real effective exchange rate, the ratio of debt to GDP, and call money rates on the other hand. However, the results show that the stockpile of foreign exchange reserves in the GCC countries is not sensitive to nominal effective exchange rates, neither to the ratio of imports to GDP, and nor to interest rates on the US Dollar. Furthermore, the study shows a robust and positive link between foreign exchange reserves and oil prices on the one hand and economic growth in these countries on the other hand.