Uncertainty of oil export often affects the other major economic sectors. This is not only the case in Iran, but most oil exporting countries are facing the same problem. In order to overcome the problem of changes in oil price & losses due to this, most countries have established a foreign exchange fund To this end, Iran has also established such a reserve fund. In this paper first, we have tried to review the record of foreign exchange fund in different countries. Secondly, we have discussed the losses and negative effects of uncertainty of oil revenues on economic growth. Hence, we have used a production function, which is derived and explained on the basis of economic growth rate. In such a function, growth rate of national production is a function of labor and capital growth. In the mean time the capital growth rate, which represents the public and private investment seems to be highly dependent on oil revenues. Accordingly, we have measured the uncertainty of oil revenues and its impact on economic growth by measuring the effects on uncertainty in oil revenues on capital growth rate. the findings show that uncertainty of oil revenues has had a significant negative effect on economic gowth during 1966-2000.