Exxon Mobil Corporation (NYSE: XOM) is the world's biggest publicly traded oil and gas company, and one of the world's biggest companies in any industry. It reported consolidated revenue of more than $394 billion in 2014 across its worldwide upstream and downstream oil and gas operations. As of October 2015, it has a market capitalization of about $309 billion.

Exxon Mobil's core businesses include oil and gas exploration and production, petroleum refining and chemical production, and the marketing of petroleum and chemical products. Petroleum products are primarily marketed under the Exxon brand in the United States, while the company's Esso brand is used in most international markets. The Mobil and Mobil 1 brands are used in the U.S. and internationally.

Many of Exxon Mobil's core operations are organized under international subsidiaries, including ExxonMobil France Holding SAS, ExxonMobil Australia and Esso Petroleum Co. Ltd. in the United Kingdom. In addition to its core subsidiaries, Exxon Mobil owns numerous other companies, including wholly owned subsidiaries, joint ventures and affiliates.

1. Imperial Oil Ltd.

Imperial Oil, Ltd. is a publicly listed oil and gas company in Canada. As of 2015, Exxon Mobil owns approximately 70% of the company's outstanding shares. Imperial Oil operates along the full length of the oil and gas supply chain. The company has oil and gas exploration and production operations across Canada and ranks as the biggest oil refiner in the country. It is also one of the largest chemical producers in Canada. Additionally, Imperial Oil markets petroleum products through its network of more than 1,700 gasoline service stations operating under Exxon Mobil's Esso brand.

2. XTO Energy, Inc.

XTO Energy, Inc. is an oil and gas drilling company in the U.S. It specializes in extracting natural gas from shale formations, often using a process known as hydraulic fracturing. The company has operated as a wholly owned subsidiary of Exxon Mobil since 2010. The merging of the two companies lifted Exxon Mobil into the position as the top natural gas producer in the U.S. As of 2015, XTO Energy holds more natural gas reserves than any other U.S. company. XTO Energy has ownership stakes in approximately 40,000 natural gas and oil wells located across the country.

3. Mobil Producing Nigeria Unlimited

Mobil Producing Nigeria Unlimited (MPN) is one of the largest oil exploration and production companies in Nigeria, which itself is the biggest oil-producing country in Africa. MPN operates in a joint venture with the state-owned Nigerian National Petroleum Corporation. MPN holds a 40% stake in the joint venture, while the Nigerian federal government holds the remaining 60%. In 2014, the joint venture produced more than 500,000 barrels of oil per day, more than 20% of total Nigerian production. Plans are in place to raise production to more than 1 million barrels per day.

4. RasGas Company Ltd.

RasGas Company Ltd. is a natural gas producer headquartered in the Middle Eastern country of Qatar. Qatar was the world's fourth-biggest natural gas producer and its second-biggest natural gas exporter in 2013, the most recent year for which global data is available. RasGas was responsible for more than 45% of Qatar's natural gas exports in 2014, equivalent to about 35 million tons, which was shipped primarily to countries in Asia and Europe. RasGas is a joint venture between Exxon Mobil and Qatar's state-owned oil and gas company, Qatar Petroleum. Exxon Mobil owns a 30% stake in the joint venture.

5. Aera Energy, LLC.

Aera Energy, LLC. is an oil and gas producer based in California. The company was established in 1997 and is co-owned by Exxon Mobil and Royal Dutch Shell plc. Aera Energy operates as an independent entity under the direction of its own board of managers. The company produces approximately 35 million cubic feet of natural gas and 130,000 barrels of oil per day in several California counties. It holds reserves of Californian oil and gas amounting to more than 680 million barrel of oil equivalents.