Wells drilled horizontally into tight oil and shale gas formations continue to account for an increasing share of crude oil and natural gas production in the U.S. In 2004, horizontal wells accounted for about 15% of U.S. crude oil production in tight oil formations. By the end of 2018, that increased to 96%. Similarly, horizontal wells made up about 14% of U.S. natural gas production in shale formations in 2004 and increased to 97% in 2018.
Although horizontal wells have been the dominant source of production from U.S. shale gas and tight oil plays since 2008 and 2010, respectively, the number of horizontal wells did not surpass the number of vertical wells drilled in these plays until 2017. About 88,000 vertical wells in tight oil and shale gas plays in the U.S. still produced crude oil or natural gas at the end of 2018, but the volume produced by these wells was minor compared with the volume produced by horizontal wells. Many of these remaining vertical wells are considered marginal, or stripper, wells, which will continue to produce small volumes until they become uneconomic.