Southwest Gas Corporation is engaged in the business of purchasing, distributing, and transporting natural gas in portions of Arizona, Nevada, and California. The Company is composed of two business segments: natural gas operations (Southwest or the natural gas operations segment) and construction services. Southwest is the distributor of natural gas in Arizona, selling and transporting natural gas in central and southern Arizona, including the Phoenix and Tucson metropolitan areas. NPL Construction Co. (NPL), a wholly owned subsidiary, is a full-service underground piping contractor that provides utility companies with trenching and installation, replacement, and maintenance services for energy distribution systems. As of December 31, 2010, Southwest purchased and distributed or transported natural gas to 1,837,000 residential, commercial, and industrial customers in geographically diverse portions of Arizona, Nevada, and California.