A worker walks up to the floor of Orion Drilling Co.'s Perseus drilling rig near Encinal in Webb County, Texas. The Perseus is drilling for oil and gas in the Eagle Ford Shale Play, a sedimentary rock formation under an area of south and east Texas. (Eddie Seal/Bloomberg News)

The geological marvel known to Texas oilmen as the Eagle Ford Shale Play is buried deep underground, but at night you can see its outline from space in a twinkling arc that sweeps south of San Antonio toward the Rio Grande.

The light radiates from thousands of surface-level gas flares and drilling rigs. It is the glow of one of the most extravagant oil bonanzas in American history, the result of the drilling technique known as hydraulic fracturing, or fracking.

Curving south and west, the lights suddenly go black at Mexico’s border, as if there were nothing on the other side.

This is a reflection of politics, not geology. The Eagle Ford shale formation is believed to continue hundreds of miles into Mexico, where it is known as the Burgos Basin. But while more than 5,400 wells have been sunk on the Texas side since 2008, Mexico has attempted fewer than 25.

A landmark energy bill approved by Mexico’s Congress in December is aimed at correcting this disparity. It has opened the country’s oil industry to private and foreign investment for the first time in 75 years, with the goal of bringing in new technology, expertise and a risk-taking culture long missing at the state oil monopoly, Pemex.

Lawmakers will be hashing out the nuts and bolts of the law over the coming weeks, but expectations are that U.S. and other global companies will be able to bid on oil and gas projects by the end of this year, beckoning the fracking crews across the border — into some of Mexico’s most violent areas.

“The United States and Canada are exploiting their shale resources on a massive scale, and we’re still in the prospecting stage,” Gustavo Hernandez, the director of exploration and production at Pemex, said in an interview. “But we believe the volumes we have are enormous.”

Pemex estimates that Mexico’s shale formations hold the energy equivalent of 60 billion barrels of oil, an amount exceeding the entire volume the country has pumped out by conventional means since 1904.

Natural gas is thought to be especially plentiful. In a 2013 survey, the U.S. Energy Information Administration ranked Mexico’s reserves of shale gas as the world's sixth-largest after China, Argentina, Algeria, the United States and Canada.

A glut of gas production in Texas has pushed prices so low that drilling for gas alone is no longer profitable, and much of it is simply burned off, or “flared,” as it comes out of the ground.

Despite Mexico’s abundant resources, the country’s soaring demand for electricity and meager pipeline infrastructure have left it dependent on imported gas to cover roughly a third of its needs. In some parts of the country, natural gas prices are four times as high as those in the United States.

It is one reason Mexican officials say the shale reserves are crucial to the country's economic and energy development, while advancing the broader goal of “North American energy independence” — making the entire free-trade zone self-sufficient for its fuel needs. Cross-border pipelines are also being added.

With cheaper gas, Mexico could lower electricity costs at the manufacturing and assembly plants that have become a pillar of the nation's economy and that are increasingly competitive with China’s.

“This is critical to the re-industrialization of North America,” said Javier Treviño, the head of the energy commission in the lower house of Mexico’s Congress. “Mexico needs to develop these resources, or else we’ll be left behind.”

But the big money is in oil, not gas.

A new Texas oil rush

In Texas, fracking on the Eagle Ford Shale Play — “Eagleferd” in local parlance — has triggered an oil rush as rich as any other in the state’s history. After just four years, the formation has surpassed more than a million barrels of oil per day, making it the second-most productive in the country, after the Permian Basin of West Texas and ahead of North Dakota’s Bakken shale formation.

The shale boom is the main reason the United States is challenging Saudi Arabia and Russia to become the world’s top oil producer. Texas pumps more than a third of U.S. output, and on its own the state would rank as the world’s ninth-largest oil producer.

The surge has transformed long-blighted south Texas towns such as Cotulla, halfway between Laredo and San Antonio, into places of frenzied construction and quick fortune. A three-bedroom house in town rents for $6,000 a month, but most oil-field workers — arriving from as far away as Alaska — sleep in RVs and campers.

“You put in a couple years here, and you’re set,” said Carla Thorton, 31, who drove down with her husband from Mississippi two years earlier and has lived in a campground ever since. Her husband works “seven 12s,” she said — 12 hours a day, seven days a week.

“If you want to buy a house or a truck, this is how you do it,” Thorton said.

Less clear is whether the U.S. contractors who have poured into south Texas would be willing to take their expertise into Mexico if the money is good enough — or the Eagle Ford ever slows down.

The biggest interest in Mexico’s energy overhaul is expected to come from large global companies such as Exxon Mobil and Shell that have the capital and equipment to hunt the most lucrative prize: huge oil fields deep under the Gulf of Mexico.

Developing northern Mexico’s shale beds could take much longer.

The reason, experts say, is that fracking is a completely different industry, dominated by smaller, independent companies and nimble contractors that can provide specialized equipment and services at precise moments in the drilling process.

Mexico has few of these things, and the willingness of foreign companies to test their fortunes in the wilds of its northern borderlands remains unknown. The region is almost totally lacking in the pipelines, highways and other infrastructure that spread across south Texas, and Mexico’s shale beds sit beneath some of the most lawless parts of the country.

Then there is the problem of water. Fracking requires huge amounts of it, and northern Mexico is in the grips of a protracted drought.

Mexican geologists and petroleum engineers say they will worry about water later. They will bring a pipeline from the sea if they have to, or from wetter coastal regions. The important thing is to first figure out how much oil and gas they have.

Danger zone

Along a flat, baked expanse of scrubland south of the Mexican border city of Reynosa, Pemex engineers work alongside a fracking crew of 50 men in bright red roughneck suits that resemble baby pajamas, emblazoned with the logo of the global oil-field service firm Weatherford International.

The company and other international firms have been working for years in Mexico under the old model, earning a set fee from Pemex rather than a percentage of production. Once the new law takes effect, foreign operators will finally get their wish — a chance to obtain licenses to drill on their own.

It is costly, highly technical work. Clustered around the well, Batial-1, are dozens of trucks, noisy generators, acid vats and storage tanks for the sludgy wastewater coming out of the hole. From a tall crane, engineers feed a flexible steel tube 8,000 feet into the earth, then angle it 4,000 feet horizontally, allowing them to blast a mix of water, sand and chemicals at pressures so powerful that the rock shatters, squirting out oil and gas.

“Unless we fracture, this oil doesn’t even exist,” said Pemex geologist Jose Galicia.

The site is a unique kind of Mexican man camp, where crews work round-the-clock in the company of cattle and goats browsing along the edge of the fence line. The oil workers have been here more than a month but cannot leave, not even to go into the nearby town. It’s too dangerous.

Like many of the well sites in this part of northern Mexico, the Batial-1 is in Zeta country. The cartel specializes in kidnapping and extortion, and when Pemex geologists and survey crews need to look for new well sites, they often travel in the company of a military escort. A group of Weatherford employees came under fire at their hotel in the nearby town of Ciudad Mier this month during a cartel gun battle, though none of the workers were hit.

While big oil companies working in countries such as Nigeria and Iraq are used to dealing with such security threats, the smaller operators that specialize in fracking are not.

“You can hire private security to keep workers safe, but all of that implies cost and slows down business,” said Duncan Wood, an energy expert and the director of the Mexico Institute at the Woodrow Wilson International Center for Scholars in Washington.

“And if a company has a shipment of supplies hijacked, that’s lost time,” Wood said. “It’s something they wouldn’t have to deal with in Texas.”

Industry experts say the current rate of return on the Eagle Ford shale is so high, and the backlog of pending drilling permits so large, that it may take years for U.S. companies to begin moving crews into Mexico.

“The first step will be getting land in the right places, and the rest of the operation will follow,” said Chris Robart, a consultant at PacWest Consulting Partners in Houston. “It’ll depend how interested people are in bringing equipment over the border.”

“That part will be relatively easy,” Robart said. “After all, it’s not that far.”