Get ready for a mammoth IPO.

Saudi Arabia plans to sell up to 5 per cent of oil giant Saudi Aramco through an initial public offering, part of a broad scheme to diversify the country's economy, Reuters reports. Deputy Crown Prince Mohammed bin Salman expects Saudi Aramco to be valued at more than $2-trillion (U.S.).

Even if the oil giant was merely valued at $2-trillion, it would still be substantially larger than any firm on the S&P 500.