Researchers at the United States Geological Survey and the Arkansas government announced on Monday that they had found a trove of lithium, a critical raw material for electric vehicle batteries, in an underground brine reservoir in Arkansas.

With the help of water testing and machine learning, the researchers determined that there might be five million to 19 million tons of lithium — more than enough to meet all of the world’s demand for the metal — in a geological area known as the Smackover Formation. Several companies, including Exxon Mobil, are developing projects in Arkansas to produce lithium, which is dissolved in underground brine.

Whether lithium harvesting takes hold in the region will depend on the ability of those companies to scale up new methods of extracting the valuable battery ingredient from salty water. The processing technique that Exxon and others are pursuing in Arkansas, known as direct lithium extraction, generally costs more than more conventional methods do,?.

Energy and mining companies have long produced oil, gas and other natural resources in the Smackover, which extends from Texas to Florida. And the federal and state researchers said lithium could be extracted from the waste stream of the brines from which companies extracted other forms of energy and elements.

The energy industry, with the Biden administration’s encouragement, has been increasingly working to produce the raw materials needed for the lithium-ion batteries in the United States. A few projects have started recently, and many more are in various stages of study and development across the country.

Most of the world’s lithium is produced in Australia and South America. A large majority of it is then processed in China, which also dominates the manufacturing of electric vehicle batteries.

“The potential for increased U.S. production to replace imports has implications for employment, manufacturing and supply chain resilience,” David Applegate, the director of the United States Geological Survey, said in a statement announcing the study. “This study illustrates the value of science in addressing economically important issues.”

Federal researchers also have identified other potential resources that could produce large quantities of lithium, including the Salton Sea in Southern California, where Berkshire Hathaway Energy and other companies are working to extract lithium from hot liquid pumped up from an aquifer more than 4,000 feet below the ground by geothermal power plants.

Exxon Mobil recently drilled exploratory wells in Arkansas and was evaluating whether it could extract lithium in a cost-competitive way, Dan Ammann, the president of the company’s Low Carbon Solutions business, said in an interview last month.

“We know we have an attractive resource. We’re working on understanding that cost equation, understanding the supply-and-demand picture,” Mr. Ammann said at the time.

Exxon said last year that it??and to be churning out enough lithium by 2030 to supply more than a million electric vehicles per year.

Lithium is already extracted from brine in Chile, one of the world’s largest producers of the metal. Companies operating there typically place brine in large ponds until the liquid has evaporated, leaving behind various minerals. That process is relatively cheap, but it takes time and?.

Several companies are hoping that direct lithium extraction will allow them to more efficiently remove lithium from brine with the help of filters and other tools. Such an approach would use less land and could have a smaller environmental impact than evaporation ponds have. But it could take mining and energy companies years to perfect the technology and apply it at a large scale.