The world's biggest company is controlled by Saudi Arabia and is not listed on a stock exchange, according to new research by the Financial Times and the management consultancy McKinsey.

The FT's Non-Public 150 - the first comprehensive study of the world's largest unlisted companies - found that Saudi Aramco, the state company in charge of the country's vast oil reserves, is worth an estimated $781bn, dwarfing the $454bn market capitalisation of its rival ExxonMobil.