Saudi Aramco is working to secure billions of dollars in cheap loans from banks seeking to strengthen their ties with the oil giant before its stock listing, banking and export credit agency (ECA).

Citigroup (Citi), Standard Chartered and Sumitomo Mitsui Banking Corporation were advising on the transactions, could raise at least $5 billion to $6 billion, all with ECA-backing.

The bid to raise funds is the latest indication of Saudi Arabia’s push to ensure what could be the world’s biggest initial public offering (IPO) goes ahead in 2018.

The loans will offer slim returns - probably less than 1 percent a year - but the banks hoped to position themselves for more work as the kingdom proceeds with selling up to 5 percent of Aramco in an IPO that could value the firm at $2 trillion.