PG&E Corporation, through its subsidiaries, operates as a public utility company in northern and central California. It engages in electricity and natural gas distribution; electricity generation and transmission; and natural gas procurement, transportation, and transmission and storage operations. The company owns and operates electricity generation facilities, transmission and distribution lines, and substations; and an integrated natural gas transportation, storage, and distribution system, as well as has underground natural gas storage fields in California. It serves residential, commercial, industrial, and agricultural customers; street and highway lighting; and other electric utilities. As of December 31, 2011, the company served approximately 5.2 million electricity distribution customers and 4.3 million natural gas distribution customers, as well as 18,618 circuit miles of interconnected transmission lines and 141,000 circuit miles of distribution lines and substations for electricity; and 42,309 miles of distribution pipelines, 6,431 miles of backbone and local transmission pipelines, and 3 underground storage fields for natural gas. PG&E Corporation was founded in 1905 and is based in San Francisco, California.