The practice, known as "flaring," makes the gas bubble up along with much more valuable crude oil in the 15,000-square-mile Bakken shale field, and companies treat the gas as waste and burn it, The New York Times reports.
More than 100 million cubic feet of natural gas is flared daily -- enough to produce energy to heat a half-million homes for a day, the Times says.
Environmentalists express concerns, as the flared gas emits at least 2 million tons of carbon dioxide into the atmosphere annually -- the same amount as 384,000 cars or a medium-size, coal-fired power plant.
In North Dakota, 30 percent of the natural gas produced is burned as waste, much more than any other U.S. oil field, but flaring is common in other countries, including Russia, Nigeria and Iran.
Flaring, which is also done at the Eagle Ford shale field in Texas, could expand in Oklahoma, Arkansas and Ohio with techniques such as hydraulic fracturing -- fracturing rock with pressurized fluid -- and horizontal drilling, environmentalists and industry executives say.
"North Dakota is not as bad as Kazakhstan, but this is not what you would expect a civilized, efficient society to do: to flare off a perfectly good product just because it's expensive to bring to market," said Michael E. Webber, associate director of the Center for International Energy and Environmental Policy at the University of Texas at Austin.
Oil companies say they can't afford pipelines and plants to capture and sell the gas until they drill oil wells and find out how much gas will bubble out of the oil in the Bakken field, the biggest oil field discovered in the United States in four decades.