Now the region is in the hottest new oil play in the country, with giant oil terminals and sprawling RV parks replacing fields of mesquite. More than a dozen companies plan to drill up to 3,000 wells around here in the next 12 months.

The Texas field, known as the Eagle Ford, is just one of about 20 new onshore oil fields that advocates say could collectively increase the nation’s oil output by 25 percent within a decade — without the dangers of drilling in the deep waters of the Gulf of Mexico or the delicate coastal areas off Alaska.

There is only one catch: the oil from the Eagle Ford and similar fields of tightly packed rock can be extracted only by using hydraulic fracturing, a method that uses a high-pressure mix of water, sand and hazardous chemicals to blast through the rocks to release the oil inside.

The technique, also called fracking, has been widely used in the last decade to unlock vast new fields of natural gas, but drillers only recently figured out how to release large quantities of oil, which flows less easily through rock than gas. As evidence mounts that fracking poses risks to water supplies, the federal government and regulators in various states are considering tighter regulations on it.

The oil industry says any environmental concerns are far outweighed by the economic benefits of pumping previously inaccessible oil from fields that could collectively hold two or three times as much oil as Prudhoe Bay, the Alaskan field that was the last great onshore discovery. The companies estimate that the boom will create more than two million new jobs, directly or indirectly, and bring tens of billions of dollars to the states where the fields are located, which include traditional oil sites like Texas and Oklahoma, industrial stalwarts like Ohio and Michigan and even farm states like Kansas.

“It’s the one thing we have seen in our adult lives that could take us away from imported oil,” said Aubrey McClendon, chief executive of Chesapeake Energy, one of the most aggressive drillers. “What if we have found three of the world’s biggest oil fields in the last three years right here in the U.S.? How transformative could that be for the U.S. economy?”

The oil rush is already transforming this impoverished area of Texas near the Mexican border, doubling real estate values in the last year and filling restaurants and hotels.

“That’s oil money,” said Bert Bell, a truck company manager, pointing to the new pickup truck he bought for his wife after making $525,000 leasing mineral rights around his family’s mobile home. “Oil money just makes life easier.”

Based on the industry’s plans, shale and other “tight rock” fields that now produce about half a million barrels of oil a day will produce up to three million barrels daily by 2020, according to IHS CERA, an energy research firm. Oil companies are investing an estimated $25 billion this year to drill 5,000 new oil wells in tight rock fields, according to Raoul LeBlanc, a senior director at PFC Energy, a consulting firm.

“This is very big and it’s coming on very fast,” said Daniel Yergin, the chairman of IHS CERA. “This is like adding another Venezuela or Kuwait by 2020, except these tight oil fields are in the United States.”

In the most developed shale field, the Bakken field in North Dakota, production has leaped to 400,000 barrels a day today from a trickle four years ago. Experts say it could produce as much as a million barrels a day by the end of the decade.

The Eagle Ford, where the first well was drilled only three years ago, is already producing more than 100,000 barrels a day and could reach 420,000 by 2015, almost as much as Ecuador, according to Bentek Energy, a consultancy.

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