Imperial Oil Company Limited was incorporated in 1880 (its name changed to Imperial Oil Limited in 1919). Initially a refining and distribution company, it expanded into oil production, exploration, marketing and related activities. It was the first substantial oil company to develop out of the oil fields of southwestern Ontario and its main competition came from the American company, Standard Oil, which purchased Imperial Oil in 1898.

Despite its origins and head office in Ontario, Imperial Oil's exploration activities were predominantly in western and northern Canada. It opened the Leduc field in 1947, launching Alberta's second oil boom (after Turner Valley, where it participated through a subsidiary, Royalite Oil Company). It discovered and refined oil at Norman Wells, NWT from 1922 and participated in the wartime exploitation of the field during the Second World War, supplying the Canol Pipeline and Whitehorse Refinery from 1943. Since then, it has made major investments in high Arctic exploration and development. It is also a significant participant in heavy oil extraction, both in the Athabasca oil sand (through Syncrude) and the Cold Lake heavy oil production field.

The company developed refining operations and a chain of service stations (retail, bulk, rail, marine and aviation) across the country. It developed an international exploration company, International Petroleum, active primarily in Latin America, including Colombia and Peru. Numerous other subsidiaries have been formed to operate in business sectors related to its primary oil business, including transportation (pipeline and marine tankers), natural gas production, petrochemical products (twine, containers, fertilizers, building materials), land development, home heating, travel support (highway restaurants, etc.). It has acquired several companies, including Texaco Canada and Mobil Oil. Imperial Oil is also a major investor in related companies, primarily pipelines.