in the early 20th century, the highest production and largest known reserves of helium were in the gases produced for their hydrocarbon content. the most important of these were the hugoton, panhandle, greenwood, and keyes fields, all located in western kansas, and the panhandles of oklahoma and texas. the hugoton and panhandle fields are particularly large, covering thousands of square miles. the helium content of the gas varies greatly within some fields. in the panhandle field, helium content is highest, up to 1.3 percent or more, along the updip southwest edge, and lowest, 0.1 percent along the northeast edge.