SAN FRANCISCO – The latest domestic energy boom is sweeping through some of the nation's driest pockets, drawing millions of gallons of water to unlock oil and gas reserves from beneath the Earth's ­surface.

Hydraulic fracturing, or the drilling technique commonly known as fracking, has been used for decades to blast huge volumes of water, fine sand and chemicals into the ground to crack open valuable shale ­formations.

But now, as energy companies vie to exploit vast reserves west of the Mississippi River, fracking's new frontier is expanding to the same lands where crops have shriveled and waterways have dried up due to severe drought.

In Arkansas, Colorado, New Mexico, Oklahoma, Texas, Utah and Wyoming, the vast majority of the counties where fracking is occurring are also suffering from drought, according to an Associated Press analysis of industry-compiled fracking data and the U.S. Department of Agriculture's official drought designations.

While fracking typically consumes less water than farming or residential uses, the exploration method is increasing competition for the ­precious resource, driving up the price of water and burdening already depleted aquifers and rivers in certain drought-stricken stretches.

Some farmers and city leaders worry that the fracking boom is consuming too much of a scarce resource, while ­others see the push for ­production as an opportunity to make money by selling water while furthering the nation's goal of energy independence.

Along Colorado's Front Range, fourth-generation farmer Kent Peppler said he is fallowing some of his cornfields this year because he can't afford to irrigate the land for the full growing season, in part because deep-pocketed energy companies have driven up the price of water.

"There is a new player for water, which is oil and gas," said Peppler, of Mead, Colo. "And certainly they are in a position to pay a whole lot more than we are."

In a normal year, Peppler said he would pay anywhere from $9 to $100 for an acre-foot of water in auctions held by cities with excess supplies. But these days, energy companies are paying some cities $1,200 to $2,900 per acre-foot. The Denver suburb of Aurora made a $9.5 million, five-year deal last summer to provide the oil company Anadarko 2.4 billion gallons of excess treated sewer water.

Dropping water table

In South Texas, where drought has forced cotton farmers to scale back, local water officials said drillers are contributing to a drop in the water table in several areas.

For example, as much as 15,000 acre-feet of water are drawn each year from the Carrizo-Wilcox Aquifer to frac wells in the southern half of the Eagle Ford Shale, one of the nation's most profitable oil and gas fields.

That's equal to about half of the water recharged ­annually into the southern portion of the aquifer, which spans five counties that are home to about 330,000 people, said Ron Green, a scientist with the nonprofit Southwest Research Institute in San Antonio.

The Eagle Ford, extending from the Mexican border into East Texas, began to boom in 2011, just as Texas struggled with the worst one-year drought in its history. While conditions have improved, most of the state is still dealing with some level of drought, and many reservoirs and aquifers have not been replenished.

West Texas cotton farmer Charlie Smith is trying to make the best of the situation. He plans to sell some of the groundwater beneath his fields to drillers, because it isn't enough to irrigate his lands in Glasscock County. Smith's fields, like the rest of the county, were declared a disaster area this year by the USDA.

"I was going to bed every night and praying to the good Lord that we would get just one rain on the crop," Smith said.

"I realized we're not making any money farming, so why not sell the water to the oil companies?" said Smith, who hopes to earn several thousand dollars for each acre-foot of water he can sell. "Every little bit helps."