There are a vast number of oil companies operating and based in Canada. The majority of the oil produced, refined and marketed in the country, however, is performed by less than 20 of those companies. Research and development, or R&D, and alterations in processes, along with acquiring new technology and tools, consistently has the largest companies competing against one another to slide into the number one place.

Many Canadian producers are developing an interest in new energy technologies and the growing value of licensing rights. This has caused a shifting focus in conducting research and development to produce patents. Some oil companies utilize patents as tools to negotiate new deals.

Some of the largest and most productive oil companies in Canada are Suncor Energy, Inc. (NYSE: SU), Enbridge, Inc. (NYSE: ENB), Imperial Oil, Ltd. (AMEX: IMO), Canadian Natural Resources, Ltd. (NYSE: CNQ) and TransCanada Corp. (NYSE:TRP). (For related reading, see "10 Canadian Oil Companies Worth Your Attention")

Suncor Energy, Inc.

Suncor is the largest company, in terms of total revenue, in Canada. It has a market capitalization of nearly $42 billion. It was established in 1919 as the subsidiary of a company now known as Sunoco Inc. More than any other company, Suncor has led the development of the Athabasca tar sands. The tar sands are an area of crude oil deposits located in the northern region of Alberta that hold a potential supply of trillions of barrels of petroleum.

The company has four refineries that function at high capacity, and upstream, midstream and downstream operations. Suncor also operates nearly 2,000 gas stations around Canada. The value of the company's real estate holdings alone, where its production facilities are located, is in the billions of dollars.

Enbridge, Inc.

Enbridge is based in Calgary and is noted as one of the largest energy delivery companies in the country. It has a market cap of almost $40 billion. The main focus for the company is transportation, distribution and generation of energy throughout North America, serving Canada and the United States primarily. In these two countries, Enbridge is responsible for operating the longest crude oil and liquid hydrocarbons transportation system worldwide. Because the company is first and foremost a distributor of energy, it owns and runs the largest natural gas distribution network in Canada. Its distribution services extend to provinces such as Quebec and Ontario and to the state of New York.

The company was first incorporated by Imperial Oil in 1949 and later bought its independence and began operations under its current name. It advanced several of its largest projects in the 2000s, including the Enbridge Northern Gateway Pipelines project and the Alberta Clipper pipeline project in 2006, the latter becoming operational in 2010.

Imperial Oil, Ltd.

Imperial Oil has a market cap of over $30 billion. As of 2012, Exxon Mobil Corp. has nearly a 70% ownership stake in the company. Imperial Oil is a major producer of crude oil and natural gas and a significant petroleum refiner for Canada. It also is a petrochemical producer and marketer for the nation, with retail and supply networks from one coast to the other. The company's headquarters are in Calgary, after moving from Toronto in 2005. It has significant holdings in the Alberta Oil Sands.

Canadian Natural Resources, Ltd.

Canadian Natural Resources, or CNRL, is one of a few oil companies that is wholly Canadian. For the first 20 years of its operations, the company had little recognition, but the development of the Athabasca sands presented a perfect opportunity and thrust it into the national spotlight. CNRL not only operates in Western Canada, but has expanded operations around the world, generating billions of dollars in Europe and even more from its light crude blocks in Africa. As of July 2015, CNRL, with a market cap of $27 billion, is one of the largest natural gas and crude oil producers in the world.

TransCanada Corporation

TransCanada Corporation is among the top North American energy/oil companies, headquartered in Calgary, with a market cap of $26 billion. It is developing operations on an energy infrastructure in North America. The company’s network of pipelines is comprised of approximately 2,200 miles of oil pipelines, along with over 40,000 miles of gas pipelines connecting essentially all of the sizable gas supply pools in North America.