The Suncor Energy Centre,^[5] formerly the Petro-Canada Centre, is a 181,000-square-metre (1,950,000 sq ft) project composed of two granite and reflective glass-clad office towers of 32 floors and 52 floors, in the office core of downtown Calgary, Alberta. The Council on Tall Buildings and Urban Habitat lists the west tower (215 m or 705 ft as measured to top of the structure), as the 23rd tallest building in Canada and the 6th tallest skyscraper outside of Toronto, as of 2023^[update].^[4] The west tower overtook the Calgary Tower as the tallest free-standing structure in Calgary from its completion in 1984, until being surpassed by the neighbouring Bow in 2010.^[6] The office towers encompass 158,000 m² (1,700,000 sq ft) of rentable office space with the complex also containing 23,000 m² (250,000 sq ft) of retail and underground parking area. A glass-enclosed walkway (part of the +15 System) provides shelter and easy access to the surrounding buildings.

The building was often called Red Square in its early years, a derisive reference to its primary occupant Petro-Canada, which was a federal Crown Corporation created under Prime Minister Pierre Trudeau's National Energy Program.^[7] Following the completion of the complex in 1984, one writer for the Calgary Herald described the buildings as "a twin-towered, $200-million monument to socialism", and later Premier Peter Lougheed would blame Petro-Canada and the two towers for the collapse of the Calgary real-estate boom, in part by flooding the market.^[8] Petro-Canada was privatized in 1991 under the Brian Mulroney government and acquired in 2009 by the complex's current namesake, Suncor Energy, which continues to operate the company as a subsidiary.^[9]

Planning for the complex began in the late-1970s following the creation of Petro-Canada. Petro-Canada came to an agreement with the West German firm ARCI Inc. to jointly develop an ARCI-owned site in Calgary to host the Crown Corporation's new headquarters.^[1] ARCI Inc served as an investment corporation, which had purchased the site several years early, and continues to be owned by the German House of Arenberg.^[1] In May 1980, a $200-million design was proposed with an all-glass, three-tower design including a 25-storey tower to be completed in 1982 and a larger 50-storey tower completed later in 1983.^[10] The Calgary Planning Commission rejected the proposal in Fall 1980 as the site was not large enough for the density three towers would provide, and the all-glass design was not desirable for the city. Subsequently, Petro-Canada purchased the air rights from the neighbouring Calgary Chamber of Commerce for $2.5 million and received approval for a granite-clad two-tower design with a density bonus option of four storeys on the smaller tower.^[1]

Construction on the complex began on April 2, 1982.^[1] During construction, local controversy arose when no Canadian bids were received to supply the site with exterior granite cladding, which resulted in the use of $500,000 of Finnish granite, which was cut and polished in Italy and shipped to the Calgary site for installation.^[1] Another local controversy was the installation of bilingual signage (French and English), which Petro-Canada head office insisted upon.^[1] On January 4, 1983, the West tower reached 191 metres in height, exceeding the Calgary Tower and becoming the tallest freestanding structure in Calgary and Western Canada.^[11] The 52-storey west tower was topped off on May 26, 1983,^[12] and the complex was completed in 1984.^[1]

During construction in April 1983, one of the site's tower cranes collapsed, killing its operator.^[13][14]

In December 1998, Petro-Canada sold their remaining half interest in the complex to Gentra Inc. (former subsidiary of Brookfield Properties) for $200 million (equivalent to $310 million in 2021), which included Petro-Canada signing a 15-year lease to remain in the towers.^[15]

Major tenants of the Suncor Energy Centre include Suncor Energy Inc., Precision Drilling Corporation, Taqa North, Crescent Point Energy, Enbridge, Direct Energy, PricewaterhouseCoopers and Weatherford Canada.

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