Image source: Getty Images. The shale extraction revolution has dramatically impacted U.S. oil and gas production. By cost-effectively unlocking the hydrocarbons trapped in these tight rock formations, producers have unleashed a torrent of new fuel output. The results have been truly breathtaking, with decades-long domestic production declines dramatically reversing course in recent years: US Crude Oil Field Production data by YCharts While production has peaked and dipped due to a global oversupply leading to weaker oil and gas prices, the country sits on a now-accessible bounty of shale resources that is projected to last for decades. What are the largest shale plays? According to the U.S. Energy Information Admiration, the most important shale plays are the Bakken, Eagle Ford, Haynesville, Marcellus, Niobrara, Permian, and Utica formations. As the map below shows, they are found in the Rockies, Texas, and Appalachia. Source: EIA. While there are a several other large and emerging shale plays, these seven are currently the most prolific. Further, these areas delivered 92% of U.S. oil production growth and 100% of U.S. natural gas production growth over the past five years, and accounted for more than half of the country's output last year: Region Oil production (thousand barrels per day) Gas production (million cubic feet per day) Bakken 1,010 1,639 Eagle Ford 1,152 6,111 Haynesville 46 5,930 Marcellus 40 17,456 Niobrara 384 4,037 Permian 2,013 6,914 Utica 79 3,666 Total 4,723 45,753 Data source: EIA (As of June 13, 2015) In just a few short years, several of these shale plays have developed into world-class producers. The Permian Basin, for example, ranks second only to the Ghawar oil field in Saudi Arabia as measured by production per day. Meanwhile, the Marcellus is one of the top five natural gas fields in the world. What are the largest shale-focused companies? EOG Resources (NYSE: EOG) has quickly become one of the nation's leading oil producers thanks to its prime positions in the Bakken, Eagle Ford, and Permian formations. In fact, according to the Railroad Commission of Texas (which, by a quirk of political history, regulates natural resources and the environment), EOG Resources was the state's largest oil producer last year, averaging 255,101 barrels of oil per day -- 9.3% of Texas' output. EOG Resources also ranked as Texas' fifth-largest gas producer, accounting for 3.8% of the gas extracted. Shale-focused peer Devon Energy (NYSE: DVN) ranked as Texas' second-largest oil producer in 2015, pulling 148,688 barrels per day from the Eagle Ford and Permian formations -- 5.4% of Texas' production. It was also the second-largest natural gas producer in the state, accounting for 8.8% of gas output. ExxonMobil (NYSE: XOM) subsidiary XTO Energy was Texas' largest natural gas producer last year, accounting for 10% of production. It also ranks as the nation's largest natural gas producer, thanks to its prime position in not only Texas' shale plays but the Marcellus and Utica formations. That said, according to the Pittsburgh Business Times, XTO was only the eighth-largest producer in Pennsylvania's sections of the Marcellus/Utica plays of last year. Instead, the paper reported, the top producer in the Keystone State's shale gas plays was EQT (NYSE: EQT). Meanwhile, Chesapeake Energy (NYSE: CHK) was the top producer in Ohio, where it has been a leader in developing the Utica shale. Turning to the Rockies, Whiting Petroleum (NYSE: WLL) is the leading producer in the prolific Bakken shale -- a position it ascended to when it bought rival Kodiak Oil & Gas in late 2014 for $6 billion. In addition to that, Whiting is one of the leading developers in the Niobrara. Investor takeaway America's large shale plays have been game-changers for the energy industry. Oil and gas companies flocked to the top shale regions to unlock the bountiful resources that lie beneath. While the boom that followed led to a glut of oil and gas on the market, pushing prices lower, these basins are still saturated with hydrocarbons. Because of that, these shale plays have the potential to drive robust returns for producers in the decades ahead, once the current glut abates, once global energy producers achieve a new supply equilibrium. A secret billion-dollar stock opportunity The world's biggest tech company forgot to show you something, but a few Wall Street analysts and the Fool didn't miss a beat: There's a small company that's powering their brand-new gadgets and the coming revolution in technology. And we think its stock price has nearly unlimited room to run for early in-the-know investors! To be one of them, just click here.Matt DiLallo has no position in any stocks mentioned. The Motley Fool owns shares of Devon Energy, EOG Resources, and ExxonMobil. 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