The United States was the first country to use hydraulic fracturing commercially to extract oil and gas.
The modern technique emerged from experiments by Stanolind Oil in the 1940s. In 1949, Halliburton carried out the first two commercial hydraulic-fracturing treatments in Stephens County, Oklahoma, and Archer County, Texas. The early treatments were modest compared with later shale operations.
Hydraulic fracturing injects a high-pressure fluid into a well to create or enlarge fractures in reservoir rock. Proppants such as sand hold those fractures open so hydrocarbons can flow toward the well. Horizontal drilling and slickwater fracturing later combined to unlock extensive shale resources in the United States.
The method is not the same as acidizing, which uses acid to dissolve minerals and improve flow. It also predates the shale boom by decades; large-scale shale production expanded after improvements in horizontal drilling, completion design, and geologic targeting.