Cline Shale is an organic-rich Pennsylvanian shale and major petroleum resource in the Midland Basin of West Texas, often treated as part of the broader Wolfcamp system. Extending beneath ten counties east of Midland, it became especially important through horizontal drilling and hydraulic fracturing after 2000, although oil had been produced there earlier from vertical wells. Its rock qualities and thick productive interval made it a leading unconventional target, and estimates of recoverable oil and gas brought national attention. Its development helped drive the modern Midland Basin boom and reinforced West Texas’s central role in U.S. oil production.