In 1917 the Sun Company Inc. began doing business in Canada supplying lubricating oils, kerosene and spirits to war plants in the Montreal area.  There was no formal presence established  in Canada until 1919 when an office opened in Montreal under the name of Sun Company of Canada.  In 1920, the business grew and the company added new product lines, including fuel oil and gasoline brought in by rail from the United States.  In 1927 Blue Sunoco gasoline, a single-grade, no-lead product, replaced Sun's previous gasolines, Yale Hi-Test and Sunoco Anti-Nox.  It was advertised as "the high-powered knockless fuel at no extra price."

In 1930 Sunoco opened the first service stations in Canada in Toronto, Montreal and Quebec City.  Construction of the Sarnia refinery began in 1952 in order to supply its central Canada product needs.  The Sarnia refinery received its first crude in October 1953 and the Great Canadian Oil Sands Limited (GCOS) was also incorporated in that year.

In 1979 Suncor Inc. was formed when all the Canadian operations of Sun Company Inc. were amalgamated with Great Canadian Oil Sands Limited.   1981 saw Sun Company Inc. selling 25% of its interest in Suncor to the Province of Ontario.   In a milestone year; 1995, Sun Company Inc. of Philadelphia sold its remaining 55% interest in Suncor.  Suncor moved its head office from Toronto to Calgary considering 60% of Suncor's asset base was in Alberta.  The move to Calgary brought the head office closer to its major operations.   In 1997 Sunoco began expanding retail marketing and it has increased to this day.