Every U.S. President since Richard Nixon has promised to get America off foreign oil—and yet, American dependence on imported crude only seemed to grow. But in 2012 that changed definitively. Thanks in part to new sources of shale oil in North Dakota and Texas—as well as conservation efforts to reduce oil consumption—the U.S. has enjoyed a major domestic oil boom. By November the country was producing 6.68 million barrels of oil a day, the highest level in 18 years—enough to make it a net exporter of petroleum products. By some estimates, the U.S. might eventually overtake Saudi Arabia as the world’s biggest oil producer. But the boom has its dark side—shale drilling requires hydrofracking, which may pollute local water supplies.