5. The energy crisis did not materialize overnight. The low prices of petroleum products during the 1950s and 1960s led to the construction of energy-inefficient capital assets that strengthened the current demand for energy. Price regulations on natural gas discouraged the development of this substitute for imported oil and simultaneously encouraged high rates of usage (for example, more electricity) . Import restrictions adopted by the United States in 1959 caused a sharp decline in the price of oil in the international market and were followed by the creation of OPEC. Environmental regulations sharply increased the demand for and retarded the supply of domestic energy. All of these factors led to the vulnerability of Western nations to the pricing policies of OPEC.