Not long ago, shale drillers defied expectation and upended traditional oil markets by increasing production despite facing lower prices. However, the industry looks like it’s finally slowing down, according to Fox Business.

Although output still remains robust and could surpass the 1970 record annual average of 9.6 million barrels a day, companies are starting to tap the brakes on drilling as they confront technological, operational and financial obstacles. While the cost of labor and services keeps rising in the most popular oil fields, the innovation that made it possible for shale drillers to maintain production during periods of low prices appears to be slowing, according to experts.

Large oil companies are facing backlash from investors, worried about focusing on growth over profit. As a result, industry leaders believe U.S. shale growth may peak sooner than forecasters have predicted.

Learn more: Fox Business > U.S. Shale Juggernaut Shows Signs of Fatigue