America's shale oil boom continues to impress, with U.S. crude oil production recently surging to its highest level in 25 years.

For the week ended Dec. 6, U.S. crude output increased to 8.075 million barrels a day, up 0.8%, or 64,000 barrels a day, according to data from the U.S. Energy Information Administration (EIA). This year, domestic oil production surged by 18% -- the quickest pace of growth on record -- as energy companies become more efficient at pumping oil from shale formations.

As a result of soaring production, the nation recently achieved a major milestone, importing less oil than it produced for the first time in almost two decades. Two states in particular -- Texas and North Dakota, which together account for roughly 75% of domestic oil production growth -- deserve much of the credit in helping the nation move closer to energy independence.

Texas
The Lone Star state is the nation's top oil producer, accounting for roughly 35% of domestic crude production. After peaking at an average 3.4 million barrels per day in 1972, Texas' oil production has come roaring back in recent years, surging from roughly 1.1 million barrels per day in 2009 to more than 2.7 million barrels daily for the month of September, the most recent month for which EIA data is available.

In fact, if Texas were a country, it would be one of the top 15 oil-producing nations in the world, with a current level of production on par with OPEC heavyweights like Kuwait and Venezuela. Companies such as ConocoPhillips (NYSE:COP) and Chesapeake Energy (NYSE:CHK) are among several that have seen tremendous success in the state's Eagle Ford shale, one of the fastest-growing plays in the country.

In the third quarter, Chesapeake's Eagle Ford production averaged approximately 95,000 barrels of oil equivalent per day, up 82% year over year, while ConocoPhillips (NYSE:COP) reported Eagle Ford production of 126,000 barrels of oil equivalent per day, up 66% year over year. Both companies view the play as instrumental to their future production growth and continue to drive down well costs and drilling days to boost returns.

North Dakota
Unlike Texas, North Dakota only recently burst into the oil-production spotlight with the development of its prolific Bakken formation. Since 2005, the state's crude oil production has surged from less than 100,000 barrels per day to more than 940,000 barrels per day in October, according to data from the state's Industrial Commission.

These spectacular gains have been driven by large operators such as Continental Resources (NYSE:CLR), the play's biggest producer, as well as juniors like Kodiak Oil & Gas (NYSE:KOG), which continue to pump more and more oil from the play, while also decreasing well costs and drilling days through multiwell-pad drilling, downspacing, and other cost-saving techniques.

For instance, Kodiak reported a more than 50% sequential increase in third-quarter average daily sales volumes, which came in at 35,400 barrels of oil equivalent per day. Meanwhile, the company's average number of drilling days fell to well under 20. Some of its quickest wells in the third quarter were drilled in just less than 15 days, down from the mid-30s when it first began drilling in the Bakken back in 2008.

Similarly, Continental Resources reported third-quarter net Bakken production of 94,500 barrels of oil equivalent per day during the third quarter, up 7% from the previous quarter. At the same time, the company has slashed its well costs by $1.2 million over the past year and expects a further $500 million reduction per well next year, highlighting the continued success of efficiency improvements.

The road to energy independence 
As these examples highlight, U.S. energy companies continue to boost production while becoming more efficient in their operations. Not only has this helped them improve their returns, but it has also helped the U.S. reduce its imports of foreign oil, which have fallen by 20% since 2008.

Next year, imports of crude and other petroleum products could fall to just 28% of domestic demand, the lowest share since 1985 and less than half of their peak of 60% in 2005, according to EIA data. Combined with low domestic demand thanks to more fuel-efficient cars and a transition toward natural gas, these developments showcase a nation moving ever closer to energy independence.

Fool contributor Arjun Sreekumar owns shares of Chesapeake Energy. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.