Suncor Energy is a Canadian integrated energy company based in Calgary, Alberta. It specializes in production of synthetic crude from oil sands. Suncor ranks number 134 in the Forbes Global 2000 list.

Until 2010, Suncor marketed products and services to retail customers in Ontario through a downstream network of 280 branded as Sunoco, and 200 customer-operated retail and Diesel fuel sites. Following the acquisition of former Crown corporation Petro-Canada, Suncor converted its Sunoco stations (which were all in Ontario) to Petro-Canada sites in order to unify all of its downstream retail operations under the Petro-Canada banner throughout Canada. It also enabled the company to discontinue paying licensing fees for the Sunoco brand to Sunoco Inc. in the United States. Nationwide, Petro-Canada's upstream product supplier and parent company is Suncor Energy. Suncor also markets through a retail network of Shell, Exxon, and Mobil branded outlets in Colorado.

Suncor was founded in 1919 in Montreal as Sun Company of Canada, a subsidiary of Sun Oil (now Sunoco). In 1979, Sun formed Suncor by merging its Canadian refining and retailing interests; Great Canadian Oil Sands (a majority-owned subsidiary, which constructed and operated the first commercial plant to develop Canada's Athabasca oil sands and went on production in 1967); and its conventional oil and gas interests. In 1981, the Government of Ontario purchased a 25% stake in the company; it divested in 1993. In 1995 Sun Oil also divested its interest in the company, although Suncor maintained the Sunoco retail brand in Canada. Suncor took advantage of these two divestitures to become an independent, widely held public company.

On March 23, 2009, Suncor announced the acquisition of Petro-Canada. This merger created a company with a combined market capitalization of C$43.3 billion. On 4 June 2009, a 98% approval rate was reached by Suncor's shareholders for the acquisition of Petro-Canada and the Competition Bureau approved the merger on June 21, 2009. The merger with Canada's 11th largest company was completed on August 1, 2009 in a $21 billion deal to form the second-largest company in Canada (after Royal Bank of Canada) in terms of market capitalization.

On 27 June 2013, the company ranked first in a table of Canada's 100 biggest companies by revenue published by The Globe and Mail.

In October 2015, Suncor launched a hostile takeover bid for Canadian Oil Sands worth around $3.29 billion, following rejected advances earlier in the year in March and April.

On 27 April 2016, Suncor announced that they had reached a $937-million deal to acquire Murphy Oil Corp.'s five per cent stake in the Syncrude project north of Fort McMurray, Alta. This follows the takeover of Canadian Oil Sands less than a year earlier, and will increase its interest in Syncrude from just under 49 per cent to nearly 54 per cent, making it the majority shareholder of the project.

In North America, Suncor develops and produces oil and natural gas in Western Canada, Colorado, and offshore drilling in eastern Canada. Its international efforts include offshore developments in the North Sea, and conventional, land-based efforts in Libya, Syria, and Trinidad and Tobago.

Suncor operates refineries in Edmonton, Alberta; Sarnia, Ontario; Montreal, Quebec and Commerce City, Colorado. These refineries supply industrial, retail and commercial consumers. The company is also one of the largest Canadian retailers of petroleum products.

Suncor is the world's largest producer of bitumen, and owns and operates an oil sands upgrading plant near Fort McMurray, Alberta, Canada. Originally developed by Great Canadian Oil Sands, a majority-owned subsidiary of Sun Oil, it is now wholly owned by the independent Suncor. It was the first commercial development on the Athabasca oil sands, although small, earlier projects like that at Bitumount also played a role in development. The company holds a 36.75% interest in the Joslyn north oil sands project which was shelved pending an economic review by operator Total S.A. in May 2014. The company also produces conventional oil, heavy crude oil, and natural gas.

In Canada, Suncor operates refineries in Alberta, Ontario and Quebec. The company's 135,000-barrel-per-day Edmonton, refinery runs entirely on oil sands-based feedstocks and produces a high-yield of light oils. A 137,000-barrel-per-day Montreal refinery produces gasoline, distillates, asphalts, heavy fuel oil, petrochemicals, solvents and feedstock for lubricants. An 85,000-barrel-per-day refinery in Sarnia, Ontario produces gasoline, kerosene, jet and Diesel fuels. A 98,000-barrel-per-day refinery in Commerce City, Colorado produces gasoline, Diesel fuel and paving-grade asphalt.

In December 2009, Husky Energy announced that it had entered into an agreement with Suncor Energy and Suncor Energy Products to purchase 98 retail outlets in the Ontario market. These gas stations were to be converted from Sunoco to the Husky brand.

Suncor operated retail fuel operations under the brand names of Sunoco exclusively in Ontario until the merger of Petro-Canada and Suncor Energy on August 1, 2009. Suncor now sells its products under the Petro-Canada name across Canada. Suncor has also converted many Sunoco-branded gas stations to Petro-Canada stations. As of 2013, all former Sunoco branded stations are operating under either the Petro-Canada or Husky names. In the United States, it operates retail outlets in Colorado as Shell and Phillips 66, under licence from Shell Oil Company (the United States subsidiary of Royal Dutch Shell) and Phillips 66, respectively.

On April 13, 2012, Suncor Energy Products Inc. paid a $500,000 fine for being found guilty of price-fixing, by one of the company's gas stations in Ontario. This result came from a larger investigation into price-fixing by Ontario gasoline retailers.

As of August 2016, Suncor Energy owns and operates three Bombardier CRJ900ER aircraft.

According to a Pollution Watch fact sheet, in 2007 Suncor Energy's oil sands operations had the sixth highest greenhouse gas emissions in Canada. While Suncor has reduced the greenhouse gas emissions intensity of its oil sands operations by more than 50% since 1990, total greenhouse gas emissions from the company's operations have increased because of growing oil sands production.

On April 2, 2009, Suncor was fined $675,000 for failing to install pollution control equipment at its Firebag operation near Fort McMurray, Alberta in July 2006. On the same day, Suncor was fined $175,000 for dumping untreated wastewater from a company work camp near Fort McMurray into the Athabasca River in 2007.

In the United States, Suncor has also been fined by the Colorado Department of Public Health and Environment. In April 2012, a fine of $2.2 million was assessed for air pollution. Suncor failed to monitor and control emissions a number of times throughout 2009 and 2010, and numerous emissions exceeded regulations. Suncor was also cited for "failure to conduct equipment inspections, train employees, and fully develop standard procedures for operating equipment". Additionally, a benzene leak into Sand Creek was discovered in the fall of 2011. Employees at Suncor and the nearby Metro Wastewater Reclamation District Plant were exposed to benzene through the air and through drinking water.

By 2009, Suncor was working to reduce the amount of bitumen entering tailings ponds. In 2009, under the auspices of the Natural Sciences and Engineering Research Council of Canada (NSERC), Suncor teamed with the University of Alberta and Matrikon, an Edmonton-based software company, to develop separation-cell technology to potentially reduce the amount of bitumen entering tailings ponds by 50 per cent.

By 2009, Suncor operated four wind farms. These provided 147 megawatts of power, providing an annual CO2 offset of 284,000 tonnes compared to coal-generated electricity. Suncor operates an ethanol facility in St. Clair, Ontario. This ethanol is blended into retail gasoline products sold at Sunoco and some Petro-Canada service stations.

In 2007, Suncor Energy was named one of Canada's Top 100 Employers, as published in Maclean's magazine, the largest oilsands development firm to receive this honour.

In October 2008, Suncor was named one of "Canada's Top 100 Employers" by Mediacorp Canada Inc., and was featured in Maclean's newsmagazine. Later that month, Suncor was also named one of Alberta's Top Employers, which was announced by the Calgary Herald and the Edmonton Journal.