The downside is waste — lots of it. Companies produce millions of gallons of salty, chemical-infused wastewater, known as brine, as part of drilling and fracking each well. Drillers are supposed to inject this material thousands of feet underground into disposal wells, but some of it isn't making it that far.

According to data obtained by ProPublica, oil companies in North Dakota reported more than 1,000 accidental releases of oil, drilling wastewater or other fluids in 2011, about as many as in the previous two years combined. Many more illicit releases went unreported, state regulators acknowledge, when companies dumped truckloads of toxic fluid along the road or drained waste pits illegally.

State officials say most of the releases are small. But in several cases, spills turned out to be far larger than initially thought, totaling millions of gallons. Releases of brine, which is often laced with carcinogenic chemicals and heavy metals, have wiped out aquatic life in streams and wetlands and sterilized farmland. The effects on land can last for years, or even decades.

Compounding such problems, state regulators have often been unable — or unwilling — to compel energy companies to clean up their mess, our reporting showed.