codewars.com (learn_2_code)

Prior to the 1970's, because the United States had long been the world's number one producer of petroleum, American companies determined the global price of oil. In 1972, domestic oil production peaked and then began its inexorable, irreversible decline. The year before, the prerogative of setting the price of crude oil had passed into the hands of a new producer group, the Organization of the Petroleum Exporting Countries.