This year Petrochina became the first Chinese company to top the Financial Times Global 500 list of the world's biggest companies by market value. The oil and gas behemoth now outranks the likes of Exxon, Shell and flavour of the month BP, in which Petrochina is reportedly looking to invest. There have been fears, however, that the company's valuation owes far more to speculation than to its true worth. Investment guru Warren Buffett sold his shares in the company back in 2007 on the back of a surge in the share price.
Petrochina, much like Russia's Gazprom, operates as an offshoot of the Chinese government. Although groups such as Buffett's Berkshire Hathaway and Mark Mobius' Templeton Group have invested in the company, over 86 per cent of its shares are owned by the state's China National Petroleum company. It benefits from having only one competitor in the domestic market - Hong Kong based Sinopec.