Crude oil prices are determined by worldwide supply and demand. Events in crude oil markets that caused spikes in crude oil prices were a major factor in all but one of the five major run-ups in gasoline prices between 1992 and 1997, according to the National Petroleum Council study U.S. Petroleum Supply – Inventory Dynamics. Rapid gasoline price increases occurred in response to crude oil shortages caused by the Arab oil embargo in 1973, the Iranian revolution in 1978, the Iran/Iraq war in 1980, and the Persian Gulf conflict in 1990. The cost of crude oil has been the main contributor to recent increases in gasoline prices. World crude oil prices reached record levels in 2007 due mainly to high worldwide oil demand relative to supply.
Other factors contributing to higher crude oil prices include political events and conflicts in some major oil producing regions, as well as other factors such as the declining value of the U.S. dollar (the currency at which crude oil is traded globally).