A growing share of U.S. natural gas production is associated-dissolved natural gas (natural gas produced from oil wells), which is the result of increased crude oil production from low permeability, tight rock formations—Permian, Bakken, Eagle Ford, Niobrara, and Anadarko. In 2018, associated-dissolved natural gas production in these five major crude oil-producing regions was 12.0 billion cubic feet per day (Bcf/d), or about 37% of total natural gas production in these regions and about 12% of total U.S. natural gas production.