Discovered in 1918 and drilled in the 1930's, the Hugoton Gas Field was one of the largest deposits of natural gas in the world. Approximately 3000 feet deep, it extends from southwestern Kansas through the Oklahoma Panhandle and into the Texas Panhandle, covering 8500 square miles, five times the size of Rhode Island. Along with later deeper discoveries of oil and gas, this field provided landowners with royalty revenue and cheap fuel for irrigation and domestic use. Today, Texas County has nearly 8000 producing oil and gas wells, and for 75 years it has been one of Oklahoma's largest sources of revenue through taxes on oil and gas production. A pump jack is used either to pump oil from underground reservoirs or to pump ancient sea water from gas reservoirs so the gas can flow up the pipe, after which the salt water is returned through an injection well.