Petroleum in the United States has been a major industry since shortly after the oil discovery in the Oil Creek area of Titusville, Pennsylvania in 1859. The petroleum industry includes exploration for, production, processing (refining), transportation, and marketing of natural gas and petroleum products. As of 2019, the U.S. is the world's largest oil producer. The leading oil-producing area in the United States in 2014 was Texas (3.17 million barrels (504,000 m3) per day), followed by the federal zone of the Gulf of Mexico (1.40 million barrels (223,000 m3) per day), followed by North Dakota (1.09 million barrels (173,000 m3) per day) and California (0.50 million barrels (79,000 m3) per day). The oil industry extracted a record high 4.0 billion barrels of crude oil in the United States in 2018, worth an average wellhead price of US$61 per barrel. The 2018 production exceeded the previous record of 3.5 billion barrels set in 1970. 2018 oil production was more than double the production ten years earlier, in 2008. US Natural gas production achieved new record highs for each year from 2011 through 2014. Marketed natural gas production in 2014 was 74.7 billion cubic feet per day, a 44% increase over the rate of 51.9 billion cubic feet per day in 2005. Over the same time period, production of natural gas liquids increased 70%, from 1.74 million barrels per day in 2005 to 2.96 million barrels per day in 2014. In April 2015, natural gas was produced at the rate of 79.4 billion cubic feet per day. In 2014, petroleum and natural gas were the two largest sources of energy in the U.S., together providing 63 percent of the energy consumed (oil provided 35 percent and gas 28 percent). In 2008 the United States consumed 19.5 million barrels (3,100,000 m3) per day of petroleum products, of which 46 percent was gasoline, 20 percent diesel fuel and heating oil, and 10 percent liquefied petroleum gas. In 2018, the U.S. imported 11% of the petroleum it used, the lowest since 1957. The largest sources of U.S. imported oil were: Canada (40%), Saudi Arabia (11%), Venezuela (9%), Mexico (8%), and Colombia (4%). According to the American Petroleum Institute, the oil and natural gas industry supports nine million U.S. jobs and makes up seven percent of the nation's gross domestic product.