Investors monitor a screen displaying stock information at the Saudi Stock Exchange (Tadawul) following the debut of Saudi Aramco's initial public offering (IPO) on the Riyadh's stock market, in Riyadh, Saudi Arabia, December 11, 2019.

State-owned oil company Saudi Aramco said on Sunday it has exercised its "greenshoe option" to sell an additional 450 million shares, raising the size of its initial public offering (IPO) to a record $29.4 billion.

Aramco initially raised a then-record $25.6 billion in its IPO in December by selling 3 billion shares at 32 riyals ($8.53) but indicated it may sell additional shares through the over-allotment of shares.

A greenshoe option, or over-allotment, allows companies to issue more shares in an IPO when there is greater demand from participants during the initial offering.

Investors were allocated the additional shares for the option during the book-building process, Aramco said.

Aramco said "no additional shares are being offered into the market today and the stabilizing manager will not hold any shares in the company as a result of exercise of the over-allotment option."