The U.S. shale oil industry is slowing as logistical challenges including labor costs and a lack of adequate pipeline capacity pile up, the chief executives of some of the largest production and oilfield services companies have warned this week.

Evidence is accumulating that the boom in the industry that began two years ago is cooling off, particularly in what has been its incandescent center, the Permian Basin of western Texas and eastern New Mexico.

At a Barclays conference in New York this week, the chief executives of Schlumberger and Halliburton, the world’s largest and third-largest listed oilfield services companies, both highlighted a slowdown in the number of new wells being brought into production. Jeff Miller, CEO of Halliburton, talked about a “decrease in customer urgency” that had put pressure on the prices the company could charge in several parts of the U.S.