After big early promises, the Saudis have taken a more cautious approach, restricting the listing initially to Saudi Arabia in order to avoid the more rigorous disclosures that would be required in New York or London.

Despite Aramco’s big profits, oil companies are out of favor with some investors, who worry that concerns about the role of fossil fuels in climate change will eventually curb demand for Aramco’s large reserves of oil and gas.

Last month, the International Energy Agency forecast that world oil demand would flatten out in the 2030s because of increasingly efficient car engines and rising use of alternative energy sources.

In the shorter term, there are concerns that the combination of growing oil supplies from the United States, Canada, Brazil and other producers and weaker demand due to a slowing world economy may reduce Aramco’s profitability, potentially threatening its ability to pay the large dividends that it is promising investors.

The aerial attacks on Aramco facilities in September highlighted to potential investors the geopolitical risks of operating in the Persian Gulf. Iran was blamed for the attacks, which temporarily forced Aramco to cut production by more than half.

More broadly, the killing of the dissident journalist Jamal Khashoggi by Saudi agents last year has hurt the reputation of Prince Mohammed, and may repel some investors.

Still, the I.P.O. showcases the kingdom’s enormous oil wealth.

A prospectus giving Aramco’s financial results reveals some long-hidden details about the size of Saudi Arabia’s oil fields. Chief among these is a monster called Ghawar, which extends for about 120 miles in the eastern part of the kingdom. The world’s largest oil field, according to the prospectus, Ghawar has accounted for more than half of Saudi Arabia’s production, yet it still has reserves of 48 billion barrels.