The drop in energy imports was the major contributor to the United States reaching its lowest trade deficit in four years, according to a federal report released on Tuesday. By value, the U.S. energy net imports was 19 percent below its level a year ago, falling from 304 billion dollars to 246 billion dollars, the U.S. Energy Information Administration said in the report. Specifically, crude oil imports were down 16 percent year-on-year in 2013, from 310 billion dollars to 268 billion dollars, while natural gas imports fell by 14 percent, from 10.3 billion dollars to 8.8 billion dollars, the data showed. Energy accounted for 15 percent of gross U.S. goods imports in 2013 and crude oil was the largest single import by value among all goods in 2013, the report said. Meanwhile, dramatic growth in the export of refined petroleum products, such as jet fuel and gasoline, also helped reduce the trade deficit in 2013. The value of net refined exports increased 55 percent in 2013 over the prior year, reaching 33 billion dollars. Overall energy export values increased by 8 percent in 2013. The U.S. trade deficit fell to a four-year low last November since October 2009, with the trade gap falling 12.9 percent to 34.3 billion dollars. While the United States has historically been a significant net importer of both crude oil and petroleum products, stagnating domestic product demand combined with rapid growth of tight oil and shale gas output turned the country into a significant exporter of petroleum products, starting in 2011. The recent energy boom has also renewed debate over whether to open U.S. crude oil for export, which largely was banned in the aftermath of the Organization of Petroleum Exporting Countries (OPEC) oil crisis in the 1970s. In October 1973, OPEC proclaimed an oil embargo against several Western countries, including the United States, in retaliation for their support of Israel, then engulfed in a war with Arab nations. Global oil prices soon climbed to an unprecedented high, which shocked the world, particularly the oil-dependent United States.