Nearly seven miles below the Gulf of Mexico, oil company BP has tapped into a vast pool of crude after digging the deepest oil well in the world, according to the Associated Press. The Tiber Prospect is expected to rank among the largest petroleum discoveries in the United States, potentially producing half as much crude in a day as Alaska''s famous North Slope oil field. The company''s chief of exploration estimated that the Tiber deposit holds between 4 billion and 6 billion barrels of oil equivalent, which includes natural gas. That would be enough to satisfy U.S. demand for crude for nearly one year. But BP does not yet know how much it can extract. The Tiber well is about 250 miles southeast of Houston in U.S. waters. At 35,055 feet, it is as deep as Mount Everest is tall, not including more than 4,000 feet of water above it. Drilling at those depths shows how far major oil producers will go to find new supplies as global reserves dwindle, and how technology has advanced, allowing them to reach once-unimaginable depths. Deep-water operations are considered to be the last frontier for pristine oil deposits, and the entire petroleum industry is sweeping the ocean floor in search of more crude. BP needs to invest years of work and millions of dollars before it draws the first drop of oil from Tiber. Such long waits are not uncommon. Projects like the Tiber well will not reduce U.S. dependency on foreign oil, which continues to grow. But new technology does permit access to major oil finds closer to U.S. shores. Because it''s close to home, Tiber would be especially attractive to refiners in America, where the government wants to cut down on oil imports from the Middle East. It''s an expensive process. A production platform costs more than $1 billion to build. Drilling a deep-water well can add another $100 million, and if crude is located, it could cost another $50 million to bring the oil to the surface. BP''s discovery is the latest in what''s called the "lower tertiary" region, an ancient section of rock in the Gulf that is roughly 300 square miles and formed between 24 million and 65 million years ago. Chevron Corp. drilled one of the first wells in the region in 2001, followed by more than a dozen others from companies such as Royal Dutch Shell, Australian oil company BHP Billiton, BP and Total SA, according to the U.S. Department of Interior''s Minerals Management Service. BP has a 62 percent working interest in the Tiber well. Petrobras owns 20 percent while ConocoPhillips owns 18 percent.