The East Texas Oil Field is a large oil and gas field in east Texas. Covering 140,000 acres (57,000 ha) and parts of five counties, and having 30,340 historic and active oil wells, it is the second-largest oil field in the United States outside Alaska, and first in total volume of oil recovered since its discovery in 1930. The GWDB contains well information including location, depth, well type, owner, driller, construction and completion data, aquifer, water-level and water quality data. This database, thanks in part to the cooperation from private well owners and public agencies, is one of the most comprehensive statewide groundwater databases in the entire The Texas Water Development Board (TWDB) Groundwater Database (GWDB) contains information on selected water wells, springs, oil/gas tests (that were originally intended to be or were converted to water wells), water levels, and water quality to gain representative information about aquifers in Texas to support water planning from a local to a more regional perspective.