Pennsylvania is home to the Marcellus Shale, a massive underground rock formation rich in natural gas resources.

The Marcellus Shale spans several states in the U.S., but it is most prominent in Pennsylvania, where it serves as a major source of natural gas. This shale formation has become a significant player in the U.S. energy industry, especially with the rise of hydraulic fracturing (fracking) technology. The extraction of natural gas from Marcellus Shale has greatly boosted energy production, contributing to the U.S. becoming a major natural gas exporter. However, the process has sparked debates about its environmental impact, especially regarding water contamination and air quality.