Following the dramatic oil price increases by the Organization of Petroleum Exporting Countries (OPEC) in late 1973 and 1974, average prices remained fairly stable through 1978 in nominal dollar terms. However the purchasing power of OPEC oil as measured by the U.S. implicit GNP deflator or the price deflator for consumption fell substantially between the first quarter of 1974 and the end of 1978, and teh value of the dollar fell significantly versus a weighted average index during the same period. Ths contrasts strongly to the experience since the end of 1979 in which OPEC price increases have greatly outpaced the rate of inflation and exchange rate flucations, causing a more than doubling of the real oil price during the subsequent eighteen months.