Who are the richest oil and gas billionaires around the world? Offshore-technology.com has released a list of the top 10.

Charles & David Koch, USA

Charles Koch, CEO of Koch Industries, and his brother executive vice president David Koch, of Koch Industries have an estimated net worth of $40.6bn each, making them the richest Oil & Gas billionaires and the world's sixth richest overall.

The Koch brothers together hold 84% stake in Koch Industries whose oil and gas business subsidiaries include the Flint Hills Resources, which operates refineries in Alaska, Minnesota and Texas.

Koch Pipeline Company owns or operates about 4,000 miles of pipelines in the US, while Koch Alaska Pipeline Company owns majority stake in the Colonial Pipeline Company. Koch Exploration Company acquires, develops and trades hydrocarbon properties in the US, Canada and Brazil.

Mukesh Ambani, India

Mukesh Ambani, the chairman and 44% shareholder of India's biggest private sector company Reliance Industries, has a net worth of $22.6bn. He is also the richest person in India and ranks 27th among the world's richest billionaires.

Reliance Industries holds interests in petroleum exploration, production, refining, marketing as well as petrochemicals, textiles, telecommunication and retail businesses. It operates the world's biggest refinery, Jamnagar oil refinery and owns India's biggest natural gas field KG-D6 in the Krishna-Godavari Basin in Bay of Bengal.

Harold Hamm, USA

With a net worth of $19.2bn, Harold Hamm, the chairman and the CEO of Continental Resources is the world's third richest oil and gas billionaire. Hamm holds a 70% stake in the company and is among the top 40 richest billionaires in the world.

Continental Resources, one of the top ten independent oil producing company in the US, produces nearly 150,000 of crude oil per day. The majority of its production comes from the Bakken and Three Forks reservoirs located in Montana and North Dakota. The company's proven reserves at the end of 2013 stood at approximately one trillion barrels of oil equivalent.

Mikhail Fridman, Russia

Mikhail Fridman, one of the original founders and controlling share holders of Alfa Group, Russia's biggest financial and industrial investment group holds interests in a diverse range of businesses including oil and gas, commercial and investment banking, asset management, insurance, retail and telecommunications. He has a net worth of approximately $16.9bn.

Alfa Group sold its 25% stake in the Russian oil company TNK-BP to Rosneft for $13.86bn in March 2013 and created a new investment vehicle called LetterOne Holdings in Luxembourg using proceeds from the sale. The new company holds the group's foreign assets and handles foreign acquisitions especially in oil, gas and telecommunications industries.

Leonid Mikhelson, Russia

Leonid Mikhelson, who owns 25% stake in the Russian natural gas producing company Novatek, has a net worth of $14.8bn. Mikhelson also holds significant stakes in the chemical holding company Sibur and the bank Pervy Obyedinenny.

Novatek produced 62.2 billion cubic meters of natural gas in 2013, accounting for 9.3% of total Russian natural gas production. Three gas fields namely, Yurkharovskoye, East-Tarkosalinskoye and Khancheyskoye accounted for more than 80% of total production volumes during the year.

Gennady Timchenko, Russia

Gennady Timchenko, the sole shareholder of Volga Group that mainly invests in energy, transport and infrastructure assets, has a net worth of $14.5bn. The 61-year old Russian businessman had also co-owned the energy trading company Gunvor Group until he sold his 43% stake to his business partner Torbjorn Tornqvist in March 2014.

Volga Group holds 23% stake in the Russian natural gas producer Novatek, 50% stake in Petromir which operates Angaro-Lenskoe gas field in the Irkutsk region and 80% stake in Transoil, one of the biggest private companies in the country.

Mohammed Al Amoudi, Saudi Arabia

Mohammed Al Amoudi, the chairman, CEO and the sole owner of MIDROC, an international holding company with substantial interests in petroleum, agribusiness, construction, tourism, as well as trade and investment, has a net worth of $14.4bn and is the second richest person in the country.

MIDROC owns 70% stake in National Oil Ethiopia and maintains major petroleum refining and retail investments in Sweden, Saudi Arabia, Morocco and Lebanon, through its subsidiary CORRAL Petroleum Holdings. The company also owns the Swedish oil and gas company Svenska Petroleum Exploration. MIDROC owns and operates approximately 1,000 petrol stations in Sweden, Saudi Arabia and Lebanon.

Vagit Alekperov, Russia

Vagit Alekperov, the president and the biggest shareholder of Russia's biggest independent oil company Lukoil, is estimated to have a net worth of $13.2bn. The 63-year old Alekperov ranks as the seventh richest billionaire in Russia.

Lukoil's proven reserves as of 2013 stood at 13.38 billion barrels of oil and 23.48 trillion cubic feet of gas. The company produced 1.81 million barrels of oil and 396,000 barrels of oil equivalent (boe) per day in 2012 from 25,873 oil wells and 312 gas wells.

German Khan, Russia

At $11bn, German Khan, one of the founders and controlling share holders of Alfa Group, is the world's ninth richest billionaire in oil and gas. Alfa Group is Russia's biggest financial and industrial investment group holding interests in oil and gas, commercial and investment banking, asset management, insurance, retail and telecommunications.

German Khan received $3.3bn in cash from the sale of oil company TNK-BP, in which Alfa Group sold 25% stake to Rosneft in 2013. He invested the same money in LetterOne Holdings, a new holding company created by Alfa Group shareholders to invest in foreign oil and gas assets.

Carrie Perrodo & Family, France

Carrie Perrodo & family of France who inherited Perenco, an independent oil and gas company operating in 15 countries, are estimated to have a net worth of $11bn. Hubert Perrodo, the founder of Perenco, died in 2006 and his son Francois currently chairs the family-owned company.

Perenco produces about 375,000 barrels of oil equivalent per day (boepd) from its hydrocarbon exploration and production operations in Africa, Latin America, Turkey, United Kingdom and Vietnam.