The world’s biggest initial public offering—that of Saudi Aramco—was supposed to go ahead at one of the great stock exchanges this year. However, according to a Financial Times report, it’s probably not going to happen until next year at the earliest.

The FT‘s report suggests that part of the problem is the valuation that crown prince Mohammed bin Salman wants to see: $2 trillion. The oil giant’s advisers are apparently struggling to make that happen. Wall Street has previously suggested something between $1-1.5 trillion is more reasonable.

Concurrently, while Saudi officials had previously indicated that the preliminary work for the IPO was all done, Saudi Aramco CEO Amin Nasser said Thursday that it would only be completed in the second half of this year.

Saudi Arabia’s idea is to sell 5% of Saudi Aramco in the IPO, which would take place simultaneously on the country’s Tadawul exchange and another international exchange—London, Hong Kong and New York are all vying for the honor. Prince Mohammed reportedly favors New York, while his advisers are worried about the regulatory scrutiny that a U.S. listing would bring.

The IPO wouldn’t just bring in up to $100 billion (if the prince gets his way) and make Saudi Aramco the most valuable company in the world; it would also end almost four decades of complete state control over the company, which is properly known as the Saudi Arabian Oil Co.

The flotation is the centerpiece of Prince Mohammed’s vision for reforming the country, with the potential to fill the coffers of the Saudi public investment fund and create a more sustainable economy.

If it goes ahead, the IPO will also make a lot of money for the investment banks involved in the process—a fifth of a percent of the money raised, but potentially still somewhere around $200 million. JPMorgan, Morgan Stanley and HSBC are coordinating things, while other banks are expected to hop on board.

“Saudi Aramco continue to review options for the listing,” the company told Fortune in a statement. “In addition to listing on Tadawul, the home exchange, a range of international options are being held under active review. Appropriate decisions will be made in due course.”