Mitchell achieved the first highly economic fracture completion of the Barnett Shale in 1998, by using slick-water fracturing.[35][2] According to the United States Geological Survey: "It was not until development of the Barnett Shale play in the 1990s that a technique suitable for fracturing shales was developed"[36] Although Mitchell experimented with horizontal wells, early results were not successful, and the Barnett Shale boom became highly successful with vertical wells. 2005 was the first year that the majority of new Barnett wells drilled were horizontal; by 2008, 94% of the Barnett wells drilled were horizontal.[4]