From the Document: "In the beginning of the 21st century, natural gas prices were increasing and the United States was viewed as a growing natural gas importer. Multiple liquefied natural gas (LNG) import terminals were built while existing ones were recommissioned and expanded. However, the market conditions also drove domestic producers to innovate. As average U.S. prices peaked in 2008, domestic shale gas production was brought to market. Improvements in technologies such as hydraulic fracturing and horizontal drilling made the development of unconventional natural gas resources such as shale and other lower-permeability rock formations economically possible. Improved efficiency has lowered production costs, making shale gas production competitive at almost any price. The large amount of natural gas brought to market enabled large-scale exports from the United States. Of today's total global trade in natural gas, some 35% takes the form of LNG."
CRS Report for Congress, R45988
Congressional Research Service: https://crsreports.congress.gov/