Note: This article was originally published July 16, 2016 and updated January 7, 2017.

The shale oil extraction revolution has dramatically impacted U.S. oil and gas production. By cost-effectively unlocking the hydrocarbons trapped in these tight rock formations through fracking, 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 Chart

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 Administration, the most important shale plays are the Bakken, Eagle Ford, Haynesville, Marcellus, Niobrara, the Permian Basin, and Utica formations. As the map below shows, they are in the Rockies, Texas, and Appalachia.

Largest Shale Plays In The Us

Source: EIA.

While there are a several other large and emerging shale plays, these seven are currently the most prolific. In fact, 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 in 2015:

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 in 2015, 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.

Drilling Rig Sunset

Image source: Getty Images.

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 also 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 in 2015. 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 abundant 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 remain 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 after global energy producers achieve a new supply equilibrium.

Matt DiLallo has no position in any stocks mentioned. The Motley Fool owns shares of Devon Energy, EOG Resources, and ExxonMobil. The Motley Fool has a disclosure policy.