Many developing countries suffer from severe fluctuations in exports while others are vulnerable to sudden increases in demand for food imports consequent on diminished harvest yields. At the same time, given the considerable structural weaknesses and rigidities which characterize the economies of the developing countries and also their limited access to the international credit markets, their ability to adjust to fluctuations in their external payments without undue sacrifice of their growth objectives depends in part on the size of their reserves. However, the accumulation of reserves also has associated costs, which can be quite significant in the case of many developing countries with pressing needs for an increase in productive investment and consumption. Many of these countries have adopted restrictions on imports and payments and comprehensive systems of foreign exchange budgeting for the purpose of adjusting external payments to external receipts.