In 1973, the Organization of Petroleum Exporting Countries (OPEC) nationalized oil resources, expelled U.S. oil producers, and withheld oil supplies. As a result, the price of oil and gasoline increased by 50% within months. Almost overnight, the field of energy economics emerged. Economists began to apply supply and demand to energy concerns of national security and everyday well-being. Energy policy became an important issue as the United States set a goal of energy independence. Energy economics uses the tools of economics to analyze the supply and demand of energy.