NEW TOWN, N.D. — Across western North Dakota, hundreds of fires rise above fields of wheat and sunflowers and bales of hay. At night, they illuminate the prairie skies like giant fireflies.

They are not wildfires caused by lightning strikes or other acts of nature, but the deliberate burning of natural gas by oil companies rushing to extract oil from the Bakken shale field and take advantage of the high price of crude. The gas bubbles up alongside the far more valuable oil, and with less economic incentive to capture it, the drillers treat the gas as waste and simply burn it.

Every day, more than 100 million cubic feet of natural gas is flared this way — enough energy to heat half a million homes for a day.

The flared gas also spews at least two million tons of carbon dioxide into the atmosphere every year, as much as 384,000 cars or a medium-size coal-fired power plant would emit, alarming some environmentalists.