DUBAI: Saudi Aramco is likely to give roles to Citi, Goldman Sachs, HSBC and Samba Financial Bank for its planned initial public offering (IPO), a source familiar with the transaction said on Sunday.

The four banks would likely get these roles in addition to Morgan Stanley and JP Morgan Chase & Co. who were chosen to play a leading role in the transaction before the process was halted last year, the source said.

Aramco is preparing to sell up to a 5% stake by 2020-2021, in what could be the world's biggest IPO. It is expected to appoint the advisers on its share sale in the coming days.

Goldman Sachs and JP Morgan declined to comment. Aramco, Citi, HSBC and Samba did not immediately respond to a request for comment outside of office hours.

The IPO is a centrepiece of Saudi Arabia's economic transformation drive to attract foreign investment and diversify away from oil.

(Reporting by Hadeel Al Sayegh; Editing by David Goodman and Andrew Cawthorne) ((sylvia.westall@thomsonreuters.com; Dubai Newsroom +971 4453 6488; Reuters Messaging: sylvia.westall.thomsonreuters.com@reuters.net))