Imperial Oil Limited engages in the exploration, production, and sale of crude oil and natural gas in Canada. The company operates through three segments: Upstream, Downstream, and Chemical. The Upstream segment engages in the exploration and production of conventional crude oil, natural gas, synthetic oil, and bitumen primarily in the western provinces, the Canada lands, and the Atlantic offshore. Its primary conventional oil producing asset is the Norman Wells oil field in the Northwest Territories. The Downstream segment engages in the transportation and refining of crude oil, as well as blending, distribution, and marketing of refined products. This segment owns and operates natural gas liquids and products pipelines in Alberta, Manitoba, and Ontario, as well as holds interests in crude oil and products pipeline companies. The Chemical segment engages in the manufacture and marketing of various petrochemicals, including ethylene, benzene, aromatic and aliphatic solvents, plasticizer intermediates, and polyethylene resin through manufacturing plants in Sarnia, Ontario, Dartmouth, and Nova Scotia. As of December 31, 2011, Imperial Oil Limited had 1,904 million oil-equivalent barrels of proved undeveloped reserves. It also maintains a nation-wide distribution system, including 22 primary terminals to handle bulk and packaged petroleum products moving from refineries to market by pipeline, tanker, rail, and road transport; and sells petroleum products through approximately 1,800 Esso retail service stations, of which approximately 480 were company owned or leased. The company was founded in 1880 and is headquartered in Calgary, Canada. Imperial Oil Limited is a subsidiary of Exxon Mobil Corporation.