Dry natural gas production from shale formations in the Appalachian Basin that spans Pennsylvania, West Virginia, and Ohio has been growing since 2008, and monthly production has recently set new record highs. Production in the region reached 32.5 billion cubic feet per day (Bcf/d) in December 2020, and it averaged 31.9 Bcf/d during the first half of 2021, the highest average for a six-month period since production began in 2008. The Appalachian Basin contains two shale formations, Marcellus and Utica, which accounted for 34% of all U.S. dry natural gas production in 2021. On its own, the Appalachian Basin would have been the third-largest natural gas producer in the world the first half of 2021, behind Russia and the rest of the United States.