Permian production has quadrupled over the last eight years, in contrast with the decline of most other established oil fields, for several reasons.

Companies found ways to lower exploration and production costs in tapping the Permian’s accommodating shale. New technologies for drilling and hydraulic fracturing helped bring the break-even price for the best wells from over $60 a barrel to as low as $33.

The Permian, as vast as South Dakota, is distinct from other shale fields because of its enormous size, the thickness of its multiple shale layers — some as fat as 1,000 feet — and its proximity to refineries on the Gulf of Mexico. Some shale fields produce too much natural gas, which is worth less than oil. Others have uneven layers of rock difficult to drill through. The Permian is rich in oil, and its shales are relatively easy to tap with today’s rigs.

Today the biggest risk, at least for producers, is that too much output might drive down prices too much and jeopardize their profitability. They could also prompt another round of aggressive actions from OPEC and its new ally, Russia.

“If U.S. production grows another two million barrels a day, we could take market share, but how long would OPEC allow that to happen?” said Scott D. Sheffield, chairman of Pioneer Natural Resources, a major Permian producer. “You could have another price war.”

That may be inevitable.

As many as 15 oil and gas pipelines serving the Permian are expected to be completed by the middle of 2020, potentially increasing exports from the Gulf of Mexico fourfold to eight million barrels a day after 2021, according to a recent Morningstar Commodities Research report.